Aug30

Diffusion

The process by which particles move over time within a material due to their kinetic motion. Molecular diffusion occurs due to Brownian motion.

Drainage

The process of forcing a nonwetting phase into a porous rock.

capillary number

the relative effect of viscous forces versus surface tension acting across an interface between a liquid and a gas, or between two immiscible liquids

drop ball

A ball that is dropped or pumped through the wellbore tubulars to activate a downhole tool or device. When the ball is located on a landing seat, hydraulic pressure generally is applied to operate the tool mechanism.

bed

A layer of sediment or sedimentary rock, or stratum. This is the smallest stratigraphic unit, generally a centimeter or more in thickness. To be labeled a bed, the stratum must be distinguishable from adjacent beds.

stratum

A layer of sedimentary rock. The plural form is strata.

Blow Out Preventer or BOP

A large valve at the top of a well that may be closed if the drilling crew loses control of formation fluids. By closing this valve, the drilling crew usually regains control of the reservoir, and procedures can then be initiated to increase the mud density until it is possible to retain pressure control of the formation.

Annular Blowout Preventer (Annular BOP)

A large valve used to control wellbore fluids. In this type of valve, the sealing element resembles a large rubber doughnut that is mechanically squeezed inward to seal on either pipe (drill collar, drillpipe, casing, or tubing) or the openhole.

spinning chain

A length of ordinary steel link chain used by the drilling crew to cause pipe being screwed together to turn rapidly.

intermediate casing string

A length of pipe used below the surface casing string, but before the production casing is run, to isolate one or more zones of the openhole to enable deepening of the well. There may be several of these strings. Depending on well conditions, these strings may have higher pressure integrity than the prior casing strings, especially when abnormally pressured formations are expected during the drilling of the next openhole section.

joint

A length of pipe, usually referring to drillpipe, casing or tubing. While there are different standard lengths, the most common length is around 30 ft [9 m]. For casing, the most common length is 40 ft [12 m].

casing joint

A length of steel pipe, generally around 40 ft [13 m] long with a threaded connection at each end. ''' are assembled to form a casing string of the correct length and specification for the wellbore in which it is installed.

pin

A male threadform, especially in tubular goods and drillstring components.

choke manifold

A manifold assembly incorporating chokes, valves and pressure sensors used to provide control of flow back or treatment fluids.

contour map

A map displaying lines that include points of equal value and separate points of higher value from points of lower value. Common types of contour maps include topographic contour maps, which show the elevation of the Earth's surface; structure contour maps, which show the elevation or depth of a formation; and gross or net sand or pay maps, which show variations in the thickness of a stratigraphic unit, also called isopachs.

Wormhole

A large, empty channel that can penetrate several feet into the formation, caused by the nonuniform dissolution of limestone or dolomite by hydrochloric acid

rotary hose

A large-diameter (3- to 5-in. inside diameter), high-pressure flexible line used to connect the standpipe to the swivel. This flexible piping arrangement permits the kelly (and, in turn, the drillstring and bit) to be raised or lowered while drilling fluid is pumped through the drillstring

kelly hose OR rotary hose

A large-diameter (3- to 5-in. inside diameter), high-pressure flexible line used to connect the standpipe to the swivel. This flexible piping arrangement permits the kelly (and, in turn, the drillstring and bit) to be raised or lowered while drilling fluid is pumped through the drillstring.

drilling riser

A large-diameter pipe that connects the subsea BOP stack to a floating surface rig to take mud returns to the surface.

marine drilling riser

A large-diameter pipe that connects the subsea BOP stack to a floating surface rig to take mud returns to the surface. Without this pipe, the mud would simply spill out of the top of the stack onto the seafloor.

surface casing

A large-diameter, relatively low-pressure pipe string set in shallow yet competent formations

dipping bed

A layer of rock or sediment that is not horizontal.

Additionally, light hydrocarbons and steam move ahead of the burning front, condensing into liquids, which adds the advantages of miscible displacement and hot waterflooding.

Explain how in-situ combustion works

eccentric

Off-center, as when a pipe is off-center within another pipe or the openhole.

dead oil

Oil at sufficiently low pressure that it contains no dissolved gas or a relatively thick oil or residue that has lost its volatile components.

live oil

Oil containing dissolved gas in solution that may be released from solution at surface conditions. must be handled and pumped under closely controlled conditions to avoid the risk of explosion or fire.

cap the well

To regain control of a blowout well by installing and closing a valve on cement additivethe wellhead.

come out of the hole OR pull out of the hole OR trip out

To remove the drillstring from the wellbore.

come out of the hole OR pull out the hole OR trip out

To remove the drillstring from the wellbore.

trip out

To remove the drillstring from the wellbore.

groundwater

Water in the subsurface below the water table. This is held in the pores of rocks, and can be connate, from meteoric sources, or associated with igneous intrusions.

fresh water

Water that is low in dissolved salt (< 2000 ppm).

free water

Water that is mobile, available to flow, and not bound to surfaces of grains or minerals in rock.

formation water

Water that occurs naturally within the pores of rock. Water from fluids introduced to a formation through drilling or other interference, such as mud and seawater, does not constitute formation water. Formation water, or interstitial water, might not have been the water present when the rock originally formed. In contrast, connate water is the water trapped in the pores of a rock during its formation, and may be called fossil water.

interstitial water

Water that occurs naturally within the pores of rock. Water from fluids introduced to a formation through drilling or other interference, such as mud and seawater, does not constitute interstitial water. Interstitial water, or formation water, might not have been the water present when the rock originally formed. In contrast, connate water is the water trapped in the pores of a rock during its formation, also called fossil water.

wettability

the tendency of one fluid to spread on, or adhere to, a solid surface in the presence of other immiscible fluids

slide

1. To drill with a mud motor rotating the bit downhole without rotating the drillstring from the surface. This operation is conducted when the bottomhole assembly has been fitted with a bent sub or a bent housing mud motor, or both, for directional drilling.

horizontal tree

A Christmas tree design for subsea applications, configured with the master valves and flow-control equipment on a horizontal axis to minimize the assembly height.

cement plug

A balanced plug of cement slurry placed in the wellbore. '' are used for a variety of applications including hydraulic isolation, provision of a secure platform, and in window-millingoperations for sidetracking a new wellbore.

oxygen scavenger

A chemical agent used in some brines and completion fluids to reduce corrosion resulting from, or exacerbated by, dissolved oxygen.

Paraffin inhibitor

A chemical injected into the wellbore to prevent or minimize paraffin deposition.

gas lock

A condition in pumping and processing equipment caused by the induction of free gas. The compressible gas interferes with the proper operation of valves and other pump components, preventing the intake of fluid

migrate

For hydrocarbons to move from their source into reservoir rocks. The movement of newly generated hydrocarbons out of their source rock is primary migration, also called expulsion. The further movement of the hydrocarbons into reservoir rock in a hydrocarbon trap or other area of accumulation is secondary migration. Migration typically occurs from a structurally low area to a higher area because of the relative buoyancy of hydrocarbons in comparison to the surrounding rock. Migration can be local or can occur along distances of hundreds of kilometers in large sedimentary basins, and is critical to the formation of a viable petroleum system.

Hydrogen probe

A corrosion test instrument mainly used in sour systems (for example, hydrogen sulfide or other sulfide rich environments) to determine qualitatively or semiquantitatively the corrosion of a structure.

fracture

A crack or surface of breakage within rock not related to foliation or cleavage in metamorphic rock along which there has been no movement. A fracture along which there has been displacement is a fault. When walls of a fracture have moved only normal to each other, the fracture is called a joint. Fractures can enhance permeability of rocks greatly by connecting pores together, and for that reason, fractures are induced mechanically in some reservoirs in order to boost hydrocarbon flow. Fractures may also be referred to as natural fractures to distinguish them from fractures induced as part of a reservoir stimulation or drilling operation. In some shale reservoirs, natural fractures improve production by enhancing effective permeability. In other cases, natural fractures can complicate reservoir stimulation.

fixed choke

A device used to control the flow of fluids by directing flow through a restriction or hole of a fixed size. The fluid characteristics and the pressure differential across the choke determine the flow rate through a '' ''

tell tale

A device used to indicate the position or function of mechanical components that cannot be easily observed, such as to indicate the launch of a cementing plug or dart.

production packer

A device used to isolate the annulus and anchor or secure the bottom of the production tubing string.

cross section

A diagram of a vertical section through a volume, as opposed to the surface, "bird's eye," or plan view of a map. Cross sections are useful for displaying the types and orientations of subsurface structures and formations.

relative permeability

A dimensionless term devised to adapt the Darcy equation to multiphase flow conditions. This is the ratio of effective permeability of a particular fluid at a particular saturation to absolute permeability of that fluid at total saturation. If a single fluid is present in a rock, its relative permeability is 1.0. Calculation of relative permeability allows comparison of the different abilities of fluids to flow in the presence of each other, since the presence of more than one fluid generally inhibits flow.

lock

A downhole device, run and retrieved on slickline, that is placed and anchored within the tubing string to provide a setting point for flow-control equipment such as valves, chokes and plugs.

sand bailer

A downhole device, usually run on slickline, used to remove sand or debris from the bottom of the wellbore. In operation, an atmospheric chamber within the tool is opened to create a surge of fluids into the chamber. Debris is then held within the chamber for recovery at surface.

slip lock

A downhole lock device, run on slickline, that incorporates a slip mechanism that engages on the tubing wall to anchor the lock at the desired setting depth.

positive displacement motor (PDM)

A downhole motor used in the oil field to drive the drill bit or other downhole tools during directional drilling or performance drilling applications. As drilling fluid is pumped through this motor, it converts the hydraulic power of the fluid into mechanical power to cause the bit to rotate.

release joint

A downhole tool that is designed to part under controlled conditions. enables part of the tool string to be left in the wellbore while the running string is retrieved.

bridge plug

A downhole tool that is located and set to isolate the lower part of the wellbore. ''' may be permanent or retrievable, enabling the lower wellbore to be permanently sealed from production or temporarily isolated from a treatment conducted on an upper zone.

Coreflooding

A laboratory test in which a fluid or combination of fluids is injected into a sample of rock. Objectives include measurement of permeability, relative permeability, saturation change, formation damage caused by the fluid injection, or interactions between the fluid and the rock.

nonconformity

A geological surface that separates younger overlying sedimentary strata from eroded igneous or metamorphic rocks and represents a large gap in the geologic record.

Udden-Wentworth scale

A grade scale for classifying the diameters of sediments. Particles larger than 64 mm in diameter are classified as cobbles. Smaller particles are pebbles, granules, sand and silt. Those smaller than 0.0039 mm are clay. Several other grain size scales are in use, but the Udden-Wentworth scale (commonly called the Wentworth scale) is the one that is most frequently used in geology.

anisotropic

Having directionally dependent properties. For a crystal of a mineral, variation in physical properties observed in different directions is anisotropy. In rocks, variation in seismic velocity measured parallel or perpendicular to bedding surfaces is a form of anisotropy. Often found where platy minerals such as micas and clays align parallel to depositional bedding as sediments are compacted, anisotropy is common in shales.

Concentric

Having the same center, such as when the casing and the wellbore have a common center point and, therefore, a uniform annular dimension.

submersible drilling rig

A particular type of floating vessel, usually used as a mobile offshore drilling unit (MODU), that is supported primarily on large pontoon-like structures submerged below the seasurface.

roller cone bit

A tool designed to crush rock efficiently while incurring a minimal amount of wear on the cutting surfaces. It has conical cutters or cones with spiked teeth around them. Invented by Howard Hughes.

rotary steerable system

A tool designed to drill directionally with continuous rotation from the surface, eliminating the need to slide a steerable motor. This tool is typically deployed when drilling directional, horizontal, or extended-reach wells.

plateau

A topographic feature consisting of a large flat area at a relatively high elevation with steep sides.

matrix stimulation

A treatment designed to treat the near-wellbore reservoir formation rather than other areas of theproduction conduit, such as the casing across the production interval, production tubulars or the perforations. ''' ''' treatments include acid, solvent and chemical treatments to improve thepermeability of the near-wellbore formation, enhancing the productivity of a well.

gas drive

A primary recovery mechanism for oil wells containing dissolved and free gas, whereby the energy of the expanding gas is used to drive the oil from thereservoir formation into the wellbore.

Water drive

A primary recovery mechanism in which the pressure from free water is sufficient to move hydrocarbons out of the reservoir, into the wellbore and up to surface.

vesicular porosity

A type of porosity resulting from the presence of vesicles, or gas bubbles, in igneous rock.

sucker rod

A steel rod that is used to make up the mechanical assembly between the surface and downhole components of a rod pumping system.They are 25 to 30 ft [7 to 9 m] long and threaded at each end to enable the downhole components to be run and retrieved easily.

simultaneous operation (SIMOP)

A term used mainly on offshore platforms, or installations with multiple wellheads, where more than one wellbore is being accessed, such as where a drilling rig, slickline unit or coiled tubing unit may be operating at the same time.

backside

A term used to describe the annulus surrounding a production tubing string above the production packer.

Brownfield

An oil or gas accumulation that has matured to a production plateau or even progressed to a stage of declining production. Operating companies seek to extend the economic producing life of the field using cost-effective, low-risk technologies.

mousehole

An opening in the rig floor near the rotary table, but between the rotary table and the vee-door, that enables rapid connections while drilling. It is usually fitted underneath with a length of casing, usually with a bottom. A joint of drillpipe that will be used next in the drilling operation is placed in this opening, box end up, by the rig crew immediately after the previous connection is made. When the bit drills down and the kelly is near the rotary table, the next piece of drillpipe must be added for drilling to continue. This next piece of drillpipe is standing in this opening when the kelly is screwed into it.

acetic acid

An organic acid used in oil- and gas-well stimulation treatments.

Blow out

An uncontrolled flow of reservoir fluids into the wellbore, and sometimes catastrophically to the surface. It may consist of salt water, oil, gas or a mixture of these.

reeled tubing

Another term for coiled tubing, a long, continuous length of pipe wound on a spool. The pipe is straightened prior to pushing into a wellbore and rewound to coil the pipe back onto the transport and storage spool.

shoe track

Another term for float joint, a full-sized length of casing placed at the bottom of the casing string that is usually left full of cement on the inside to ensure that good cement remains on the outside of the bottom of the casing

surface pipe

Another term for surface casing,

tie-back string

Another term for tie-back liner, a section of liner that is run from a liner hanger back to the wellhead after the initial liner and hanger system have been installed and cemented. A tie-back liner may be required to provide the necessary pressure capacity during a flow-test period or for special treatments, and is typically not cemented in place. In some cases, a tie-back liner will be installed as a remedial treatment when the integrity of the intermediate casing string is in doubt.

Minimum miscibility pressure (MMP)

At constant temperature and composition, the lowest pressure at which first- or multiple-contact miscibility (dynamic miscibility) can be achieved.

Minimum miscibility concentration or minimum miscibility enrichment

At constant temperature and pressure, the minimum quantity of additional components, such as intermediate-chain gases or CO2, that must be added to an injection gas to reach first-contact miscibility with a reservoir fluid at a given temperature and pressure. At minimum this condition the interfacial tension is zero and no interface exists between the fluids.

neat cement

Cement that has no additives to modify its setting time or rheological properties

tuffaceaous

Containing tuff, which is lithified volcanic ash.

vuggy

Containing vugs, which are cavities, voids or large pores in a rock that are commonly lined with mineral precipitates.

An enhanced oil recovery method in which carbon dioxide (CO2) is injected into a reservoir to increase production by reducing oil viscosity and providing miscible or partially miscible displacement of the oil.

Define CO2 flooding.

The ratio of effective permeability to phase viscosity.

Define mobility

Volume of pay contacted/total volume of pay

Define sweep efficiency as a ratio

The corrosion caused by contact with carbon dioxide [CO2] dissolved in water or by another agent other than hydrogen sulfide [H2S].

Define sweet corrosion.

A condition whereby the interface of two fluids, such as oil and water, bypasses sections of reservoir as it moves along, creating an uneven, or fingered, profile.

Define viscous fingering

It improves sweep efficiency by preventing viscous fingering of the more mobile chase/drive fluid

How does a mobility buffer work?

Surfactant molecules preferentially position themselves at the interface and thereby lower the interfacial tension. In essence they "bridge" the interface between immiscible phases.

How does surfactant lower interfacial tension?

Reservoir oil swelling can result in improved oil recovery by mobilizing residual oil trapped in inaccessible pore spaces.

How may oil swelling improve recovery?

Use of KCl (potassium chloride) based brines in drilling mud. Use of oil-based mud.

How might your avoid clay swelling?

Vertical displacement efficiency

In a displacement process, the ratio of the cumulative height of the vertical sections of the pay zone that are contacted by injection fluid to the total vertical pay zone height.

Areal sweep efficiency.

In a reservoir waterflood or other fluid injection using a well pattern, the fraction of the pattern area from which reservoir fluid is displaced by the injected phase at the time of breakthrough.

free water

In cementing, any water in the slurry that is in excess of what is required to fully hydrate the Portland cement and other additives.

Mobility buffer

In chemical flooding, a fluid stage, normally water thickened with a polymer, pumped between the micellar or alkaline chemical solution and the final water injection.

Soak phase

In cyclic steam injection, the second phase between the steam-injection phase and the production phase.

washover pipe

In fishing operations, a large-diameter pipe fitted with an internal grappling device and tungsten carbide cutting surfaces on the bottom. This pipe can be lowered over a fish in the wellbore and to latch onto and retrieve the fish.

Give the most common reasons for running casing in a well:

1) protect fresh-water aquifers (surface casing)

Reasons for running casing in a well

1) protect fresh-water aquifers (surface casing)

slips

1. A device used to grip the drillstring in a relatively nondamaging manner and suspend it in the rotary table. This device consists of three or more steel wedges that are hinged together, forming a near circle around the drillpipe.

tight hole

1. A section of a wellbore, usually openhole, where larger diameter components of the drillstring, such as drillpipe tool joints, drill collars, stabilizers, and the bit, may experience resistance when the driller attempts to pull them through these sections. 2. A well that the operator requires be kept as secret as possible, especially the geologic information. Exploration wells, especially rank wildcats, are often designated as tight. Unfortunately, this designation is of questionable benefit in keeping the data secret.

*adjustable choke

1. A valve usually used in well control operations to reduce the pressure of a fluid from high pressure in the closed wellbore to atmospheric pressure. It may be adjusted (opened or closed) to closely control the pressure drop.

fish

1. Anything left in a wellbore. It does not matter whether it consists of junk metal, a hand tool, a length of drillpipe or drill collars, or an expensive MWD and directional drilling package. Once the component is lost, it is simply referred to this term.

hopper

1. In general, a funnel-shaped device used to transfer products. It is often at the bottom of any container for holding or using bulk products, especially drilling fluid additives and cementing material.

conformable

1. Parallel strata that have undergone a similar geologic history, deposited in succession without interruption.

transpression

The simultaneous occurrence of strike-slip faulting and compression, or convergence, of the Earth's crust. In areas of transpression, rocks can be faulted upward to form a positive flower structure. Areas of strike-slip faulting in rifting or diverging crust are experiencing transtension, in which rocks can drop down to form a negative flower structure.

transtension

The simultaneous occurrence of strike-slip faulting and extension, rifting, or divergence of the Earth's crust. In areas of transtension, rocks can be faulted downward to form a negative flower structure. Areas of strike-slip faulting in converging crust are experiencing transpression, in which rocks can be faulted upwards to form a positive flower structure.

drilling rate

The speed at which the drill bit can break the rock under it and thus deepen the wellbore. This speed is usually reported in units of feet per hour or meters per hour.

axial surface

In folded rocks, the imaginary surface bisecting the limbs of the fold. This is called the axial plane when the fold is symmetrical and the lines defined by the points of maximum curvature of each folded layer, or hinge lines, are coplanar.

differential pressure

In general, a measurement of fluid force per unit area (measured in units such as pounds per square in.) subtracted from a higher measurement of fluid force per unit area.

hook

The high-capacity J-shaped equipment used to hang various other equipment, particularly the swivel and kelly, the elevator bails or topdrive units. It is attached to the bottom of the traveling block and provides a way to pick up heavy loads with the traveling block.

crest

The highest point of a wave, mountain or geologic structure.

offset

The horizontal displacement between points on either side of a fault, which can range from millimeters to kilometers. Perhaps the most readily visible examples of offset are features such as fences or roads that have been displaced by strike-slip faults, such as the San Andreas fault of California, USA.

Casing

Large-diameter pipe lowered into an openhole and cemented in place.

casing

Large-diameter pipe lowered into an openhole and cemented in place. The well designer must design casing to withstand a variety of forces, such as collapse, burst, and tensile failure, as well as chemically aggressive brines.

Weevil

Name given to a new, completely inexperienced member of the drilling crew. Such a crewmember is stereotyped as prone to making mistakes and being injured, and typically endures pranks played on him by the drilling crew.

Reynolds number

Ratio of inertial force to viscous force acting on a fluid

rift (noun)

Region in which the Earth's crust is pulling apart and creating normal faults and down-dropped areas or subsidence.

clear brine

Saline liquid usually used in completion operations and, increasingly, when penetrating a pay zone.

Brine

Saline liquid usually used in completion operations and, increasingly, when penetrating a pay zone. It is preferred because they have higher densities than fresh water but lack solid particles that might damage producible formations

p rate

Slang for penetration rate, or the speed that the bit is drilling into the formation.

Huff and puff

Slang term for a cyclic process in which a well is injected with a recovery enhancement fluid and, after a soak period, the well is put back on production. Examples are cyclic steam injection and cyclic CO2 injection.

Duster

Slang term for dry hole

duster

Slang term for dry hole

fracture permeability

That portion of a dual-porosity reservoirs permeability that is associated with the secondary porosity created by open, natural fractures. In many of these reservoirs, fracture permeability can be the major controlling factor of the flow of fluids.

cresting

The change in oil-water or gas-oil contact profiles as a result of drawdownpressures during production. ''' occurs in horizontal or highly deviated wells and is affected by the characteristics of the fluids involved and the ratio of horizontal to vertical permeability.

progradation

The accumulation of sequences by deposition in which beds are deposited successively basinward because sediment supply exceeds accommodation. Thus, the position of the shoreline migrates into the basin during episodes of progradation, a process called regression.

Estimated-ultimate-recovery

The amount of oil and gas expected to be economically recovered from a reservoir or field by the end of its producing life.

underbalance

The amount of pressure (or force per unit area) exerted on a formation exposed in a wellbore below the internal fluid pressure of that formation. If sufficient porosity and permeability exist, formation fluids enter the wellbore. The drilling rate typically increases as an underbalanced condition is approached.

overbalance

The amount of pressure (or force per unit area) in the wellbore that exceeds the pressure of fluids in the formation. This excess pressure is needed to prevent reservoir fluids (oil, gas, water) from entering the wellbore. However, excessive pressure can dramatically slow the drilling process by effectively strengthening the near-wellbore rock and limiting removal of drilled cuttings under the bit. In addition, excess pressures coupled with poor mud properties can cause differential sticking problems.

plunge

The angle between a linear feature and a horizontal line in a vertical plane containing both lines.

azimuth

The angle between the vertical projection of a line of interest onto a horizontal surface and true north or magnetic north measured in a horizontal plane, typically measured clockwise from north.

apparent dip

The angle that a plane makes with the horizontal measured in any randomly oriented section rather than perpendicular to strike.

geopressure gradient

The change in pore pressure per unit depth, typically in units of pounds per square inch per foot (psi/ft) or kilopascals per meter (kPa/m). The geopressure gradient might be described as high or low if it deviates from the normal hydrostatic pressure gradient of 0.433 psi/ft [9.8 kPa/m].

strike

The azimuth of the intersection of a plane, such as a dipping bed, with a horizontal surface.

trend

The azimuth or orientation of a linear feature, such as the axis of a fold, normally expressed as a compass bearing.

cement

The binding material in sedimentary rocks that precipitates between grains from pore fluids. Calcite and quartz are common cement-forming minerals.

casing shoe

The bottom of the casing string, including the cement around it, or the equipment run at the bottom of the casing string. OR A short assembly, typically manufactured from a heavy steel collar and profiled cement interior, that is screwed to the bottom of a casing string.

Moho

The boundary between the crust and the mantle of the Earth, which varies from approximately 5 km [3 miles] under the midoceanic ridges to 75 km [46 miles] deep under the continents. This boundary, commonly called "the Moho," was recognized in 1909 by Croatian seismologist Andrija Mohorovicic on the basis of its abruptly higher compressional wave (P-wave) velocity.

lithosphere

The brittle outer layer of the Earth that includes the crust and uppermost mantle. It is made up of six major and several minor tectonic plates that move around on the softer asthenosphere. The lithosphere of the oceans tends to be thinner (in some oceanic areas, less than 50 km [30 miles] thick) and more dense than that of the continents (more than 120 km [70 miles] thick in places like the Himalayas) because of isostasy. The movement of the plates of the lithosphere results in convergence, or collisions, that can form mountain belts and subduction zones, and divergence of the plates and the creation of new crust as material wells up from below separating plates. The lithosphere and asthenosphere are distinguished from the crust, mantle and core of the Earth on the basis of their mechanical behavior and not their composition.

drill string

The combination of the drillpipe, the bottomhole assembly and any other tools used to make the drill bitturn at the bottom of the wellbore.

drillstem

The combination of the drillpipe, the bottomhole assembly and any other tools used to make the drill bitturn at the bottom of the wellbore.

multiphase fluid flow

The commingled flow of different phase fluids, such as water, oil and gas.

drilling contractor

The company that owns and operates a drilling rig.

operator

The company that serves as the overall manager and decision-maker of a drilling project

circulation system

The complete, circuitous path that the drilling fluid travels.

Sour corrosion

The corrosion caused by contact with hydrogen sulfide [H2S] dissolved in water.

calcite

The crystalline form of calcium carbonate and chief constituent of limestone and chalk. Calcite reacts readily with dilute hydrochloric acid [HCl], so the presence of calcite can be tested by simply placing a drop of acid on a rock specimen.

abyss

The deepest area of the ocean basins. The depositional energy is low and fine-grained sediments are deposited slowly by waning turbidity currents or from suspension in the water. The water is thousands of meters deep (>2,000 m) [>6,520 ft] so it is cold and sunlight is minimal.

Partitioning

The degree of solubilization of a solute into each of multiple immiscible phases at equilibrium. For example, a water-soluble surfactant injected as part of an enhanced oil recovery flood will partially solubilize in the oil phase.

grain density

The density of a rock or mineral with no porosity, also known as matrix density, commonly in units of g/cm3.

contract depth

The depth in a drilling well at which the drilling contractor receives a lump-sum payment for reaching a particular milestone.

carbon dioxide corrosion

The deterioration of metal components resulting from contact with a gas or solution containing carbon dioxide.

sweet corrosion

The deterioration of metal due to contact with carbon dioxide or similar corrosive agents, but excluding hydrogen sulfide [H2S]. typically results in pitting or material loss and occurs where steel is exposed to carbon dioxide and moisture.

inclination

The deviation from vertical, irrespective of compass direction, expressed in degrees.

exploration

The initial phase in petroleum operations that includes generation of a prospect or play or both, and drilling of an exploration well. Appraisal, development and production phases follow successful exploration.

inside diameter (ID)

The inner diameter. Casing, tubing and drillpipe are commonly described in terms of their inside and outside diameter (OD).

sand control

The installation of equipment or application of techniques to prevent migration of reservoir sand into the wellbore or near-wellbore area.

monkey board

The small platform that the derrickman stands on when tripping pipe.

shear stock

The material from which shear pins are typically cut.

Cement

The material used to permanently seal annular spaces between casing and borehole walls. It is also used to seal formations to prevent loss of drilling fluid and for operations ranging from setting kick-off plugs to plug and abandonment.

gauge pressure

The measured pressure within a system in which the pressure gauge reads 0 psi at nominal atmospheric pressure.

minimum restriction

The smallest diameter present in a wellbore through which a tool string must pass to enable access to the operating depth or zone of interest.

prime mover

The source of power for the rig location. On modern rigs, they consists of one to four or more diesel engines.

Annulus (Annuli)

The space between two concentric objects, such as between the wellbore and casing or between casing and tubing, where fluid can flow. Pipe may consist of drill collars, drillpipe, casing or tubing.

annular space

The space surrounding one cylindrical object placed inside another, such as the space surrounding a tubular object placed in a wellbore.

displacement

The offset of segments or points that were once continuous or adjacent. Layers of rock that have been moved by the action of faults show displacement on either side of the fault surface.

moon pool

The opening in the hull of a drillship or other offshore drilling vessel through which drilling equipment passes.

attitude

The orientation of a planar or linear feature in three-dimensional space. Planar features that are not horizontal, such as tilted strata, are described by their strike, or the azimuth of the intersection of the plane with a horizontal surface, and the dip, or the magnitude of its inclination from a horizontal reference. The trend and plunge of linear features, such as the axis of a fold, describe the azimuth of the line and its deviation from horizontal.

facies

The overall characteristics of a rock unit that reflect its origin and differentiate the unit from others around it. Mineralogy and sedimentary source, fossil content, sedimentary structures and texture distinguish one facies from another.

graveyard tour

The overnight work shift of a drilling crew. Drilling operations usually occur around the clock because of the cost to rent a rig. As a result, there are usually two separate crews working twelve-hour tours to keep the operation going.

jet nozzle

The part of the bit that includes a hole or opening for drilling fluid to exit. The hole is usually small (around 0.25 in. in diameter) and the pressure of the fluid inside the bit is usually high, leading to a high exit velocity of fluid.

cementation

The process of precipitation of cement between mineral or rock grains and forming solid clastic sedimentary rock, one phase of lithification.

total depth (TD)

The planned end of the well, measured by the length of pipe required to reach the bottom.

Plait point

The point at which the liquid and vapour portions of the binodal curve meet

Cased Hole

The portion of the wellbore that has had metal casing placed and cemented to protect the openhole from fluids, pressures, wellbore stability problems or a combination of these.

cased hole

The portion of the wellbore that has had metal casing placed and cemented to protect the openhole from fluids, pressures, wellbore stability problems or a combination of these.

Wettability

The preference of a solid to contact one liquid or gas, known as the wetting phase, rather than another.

injection pressure

The pressure at which a treatment or test fluid can be injected into the formation matrix without causing a breakdown, or fracture, of the rock matrix. This pressure is commonly described as the surface pump pressure required to achieve injection. However, since the hydrostatic pressure of the fluid column also contributes to the downhole pressure value, the downhole pressure should also be considered.

Dewpoint

The pressure at which the first condensate liquid comes out of solution in a gas condensate.

breakdown pressure

The pressure at which the rock matrix of an exposed formation fractures and allows fluid to be injected. The ''' is established before determining reservoir treatment parameters. Hydraulic fracturing operations are conducted above the breakdown pressure, while matrix stimulation treatments are performed with the treatment pressure safely below the ''''.

open flow potential

The calculated maximum flow rate that a system may provide in the absence of restrictions. The term may be qualified as relating to a specific zone, such as a perforated interval or be used in referring to theproduction capability of the well.

Recovery factor

The recoverable amount of hydrocarbon initially in place, normally expressed as a percentage.

lost circulation OR lost returns

The reduced or total absence of fluid flow up the annulus when fluid is pumped through the drillstring. Though the definitions of different operators vary, this reduction of flow may generally be classified as seepage (less than 20 bbl/hr [3 m3/hr]), partial lost returns (greater than 20 bbl/hr [3 m3/hr] but still some returns), and total lost returns (where no fluid comes out of the annulus).

mechanical skin

The reduction in permeability in the near-wellbore area resulting from mechanical factors such as thedisplacement of debris that plugs the perforations or formation matrix. Such damage in the near-wellbore area can have a significant effect on the productivity of a well.

saturation

The relative amount of water, oil and gas in the pores of a rock, usually as a percentage of volume.

depositional energy

The relative kinetic energy of the environment. A high-energy environment might consist of a rapidly flowing stream that is capable of carrying coarse-grained sediments, such as gravel and sand. Sedimentation in a low-energy environment, such as an abyssal plain, usually involves very fine-grained clay or mud. Depositional energy is not simply velocity. For example, although glaciers do not move quickly, they are capable of carrying large boulders.

hydrostatic head

The height of a column of freshwater that exerts pressure at a given depth. Some authors use the term synonymously with hydrostatic pressure.

casing thread

The threadform found on casing joints. In addition to providing mechanical or structural strength, the '''' must be compatible with the pressures and fluids associated with the application. Some advanced threadforms incorporate a gas seal.

depositional system

The three-dimensional array of sediments or lithofacies that fills a basin. Depositional systems vary according to the types of sediments available for deposition as well as the depositional processes and environments in which they are deposited. The dominant depositional systems are alluvial, fluvial, deltaic, marine, lacustrine and eolian systems.

Bit

The tool used to crush or cut rock. Most of these work by scraping or crushing the rock, or both, usually as part of a rotational motion.

crown valve

The topmost valve on a Christmas tree that provides vertical access to the wellbore.

lubricator valve

The topmost valve on a Christmas tree that provides vertical access to the wellbore.

swab valve

The topmost valve on a Christmas tree that provides vertical access to the wellbore.

nitrogen lift

The use of nitrogen gas circulated into the production conduit to displace liquids and reduce the hydrostatic pressure created by the fluid column. Is a common technique used to initiate production on a well following workover or overbalanced completion.

Azimuth

This is usually specified in degrees with respect to the geographic or magnetic north pole. Also known as the compass direction of a directional survey

make a connection

To add a length of drillpipe to the drillstring to continue drilling.

erode

To cause or undergo erosion, the wearing away of material, usually rock or steel, by the continuous abrasive action of a solids-laden slurry.

reverse circulation

To circulate fluid down the wellbore annulus, with returns being made up the tubing string. is often used to remove debris from the wellbore since the high fluid flow rate inside the tubing string enables the recovery of large or dense debris particles that are difficult or impossible to remove with conventional circulation.

close in

To close a valve to stop or isolate fluid flow. The term is most commonly applied to "closing-in the well," meaning isolation of the wellbore by closing the master valve.

correlate

To compare and fix measured depths with known features on baseline logs of the wellbore tubulars and the surrounding formation.

twist off

To part or break the drillstring downhole due to either fatigue or excessive torque.

swab

To reduce pressure in a wellbore by moving pipe, wireline tools or rubber-cupped seals up the wellbore.

Reduce SPM (strokes per minute) , reduce the size of the primary chamber

What are the measures which one will take to reduce the chances of a gas lock and fluid pound in SRP

A normal/regular injection pattern includes only one production well per pattern. An inverted pattern includes only one injection well per pattern.

What is the difference between a normal/regular injection pattern and an inverted injection pattern?

In a vaporizing drive, light and intermediate components from the oil phase enter the gas phase. By contrast, in a condensing drive, intermediate components from the gas phase enter the oil phase.

What is the difference between a vaporizing gas drive and a condensing gas drive?

Microemulsions are thermodynamically stable, representing a minimum energy state. Microemulsions form spontaneously. On the other hand emulsions form under shear upon input of external energy. They are thermodynamically unstable.

What is the difference between an emulsion and a microemulsion?

Background Gas or BGG

What is the name given to gas that is liberated downhole while drilling through a uniform lithologic interval at a constant rate of penetration. The gas is typically obtained from a suction line above the gas trap located immediately upstream of the shale shaker screens, where the gas evolves out of the mud.

Air Drilling

What is the name given to the technique whereby gases (typically compressed air or nitrogen) are used to cool the drill bit and lift cuttings out of the wellbore, instead of the more conventional use of liquids?

Since steam is lighter and more mobile than oil, gravity differences and channeling of the steam through the most permeable parts of the reservoir can create sweep efficiency problems.

Why may there be sweep efficiency problems with steam flooding?

Tie- line

a line drawn through the mixture composition on the phase diagram when it is in a two phase field, intersecting the two adjacent solubility curves, is called ______

frac job

a stimulation treatment routinely performed on oil and gas wells in low-permeability reservoirs. Specially engineered fluids are pumped at high pressure and rate into thereservoir interval to be treated, causing a vertical fracture to open. The wings of the fracture extend away from the wellbore in opposing directions according to the natural stresses within the formation. Proppant, such as grains of sand of a particular size, is mixed with the treatment fluid to keep the fracture open when the treatment is complete. Hydraulic fracturing creates high-conductivity communication with a large area of formation and bypasses any damage that may exist in the near-wellbore area.

Polyacrylamides and poly saccharides

according to larry w lake: virtually all commercially atteactive polymers fall in two generic classes, these are:

atmospheric corrosion

resulting from exposure of susceptible materials to oxygen and moisture. Is generally associated with surface storage conditions, or with upper wellbore annuli that may not be fluid-filled.

Citric acid.

Give two examples of chelating agents

vug

A cavity, void or large pore in a rock that is commonly lined with mineral precipitates.

Polysaccharide

A carbohydrate polymer composed of many monosaccharides.

hiatus

A cessation in deposition of sediments during which no strata form or an erosional surface forms on the underlying strata; a gap in the rock record. This period might be marked by development of a lithified sediment (hardground) or burrowed surface characteristic of periods when sea level was relatively low. A disconformity can result from a hiatus.

premium thread

A class of high-performance thread types that are commonly used in modern oilwell and gaswell completions.

crossflow

A condition that exists when two production zones with dissimilar pressure characteristics are allowed to communicate during production. Reservoir fluid from the high-pressure zone will flow preferentially to the low-pressure zone rather than up the production conduit unless the production parameters are closely controlled.

drape

A configuration of layers of rock that has the appearance of a fold, but might form simply through sagging or differential compaction of layers around a preexisting structure (such as a reef) or on an uneven surface.

datum

A depth reference point, typically established at the time the well is completed, against which subsequent depth measurements should be corrected or correlated.

sand

A detrital grain between 0.0625 mm and 2 mm in diameter. This is larger than silt but smaller than a granule according to the Udden-Wentworth scale. Sand is also a term used for quartz grains or for sandstone.

recorder carrier

A downhole tool used to locate or convey a downhole gauge. '' ''' may be incorporated into temporary completions, such as for testing purposes, or run on slickline for temporary placement within the wellbore.

carrier fluid

A fluid that is used to transport materials into or out of the wellbore. ''' typically are designed according to three main criteria: the ability to efficiently transport the necessary material (such as packsand during a gravel pack), the ability to separate or release the materials at the correct time or place, and compatibility with other wellbore fluids while being nondamaging to exposed formations.

multiphase fluid

A fluid, generally a liquid, comprising more than one phase, such as water- or oil-based liquids, solid material or gas.

Thief Zone

A formation encountered during drilling into which circulating fluids can be lost.

soft rock

A general term for sedimentary rocks, although it can imply a distinction between rocks of interest to the petroleum industry and rocks of interest to the mining industry.

fishing tool

A general term for special mechanical devices used to aid the recovery of equipment lost downhole. These devices generally fall into four classes: diagnostic, inside grappling, outside grappling, and force intensifiers or jars

crude oil

A general term for unrefined petroleum or liquid petroleum.

fluid invasion

A general term to describe the presence of a particular fluid in an undesirable area, such as the movement of drilling mud into a section of the reservoir formation.

Forward multiple-contact test

A laboratory test to determine the phase envelope between lean gas and oil by equilibrating a gas sample several times with fresh samples of oil. Light and intermediate components are stripped from the oil by multiple contacts with the gas. The test also indicates how many contacts are required before the gas with added components becomes miscible with the oil. The molar ratios at each contact step are typically designed using PVT simulation software that incorporates the fluid composition at each contact.

cut and thread fishing technique

A method for recovering wireline stuck in a wellbore. In this operation, the wireline is gripped securely with a special tool and cut at the surface. The cut end is threaded through a stand of drillpipe. While the pipe hangs in the wellbore, the wireline is threaded through another stand of drillpipe, which is screwed onto the stand in the wellbore. The process is repeated until the stuck wireline is recovered.

natural gas

A naturally occurring mixture of hydrocarbon gases that is highly compressible and expansible. Methane [CH4] is the chief constituent of most natural gas (constituting as much as 85% of some natural gases), with lesser amounts of ethane [C2H6], propane [C3H8], butane [C4H10] and pentane [C5H12]. Impurities can also be present in large proportions, including carbon dioxide, helium, nitrogen and hydrogen sulfide.

hydrocarbon

A naturally occurring organic compound comprising hydrogen and carbon. Hydrocarbons can be as simple as methane [CH4], but many are highly complex molecules, and can occur as gases, liquids or solids. The molecules can have the shape of chains, branching chains, rings or other structures. Petroleum is a complex mixture of hydrocarbons. The most common hydrocarbons are natural gas, oil and coal.

weevil OR worm

A new, completely inexperienced member of the drilling crew.

dog leg

A particularly crooked place in a wellbore where the trajectory of the wellbore in three-dimensional space changes rapidly. While it is sometimes created intentionally by directional drillers, the term more commonly refers to a section of the hole that changes direction faster than anticipated or desired, usually with harmful side effects.

gas sand

A porous sand layer or sand body charged with natural gas.

Casing Grade

A system of identifying and categorizing the strength of casing materials. Since most oilfield casing is of approximately the same chemistry (typically steel), and differs only in the heat treatment applied, the grading system provides for standardized strengths of casing to be manufactured and used in wellbores.

well stimulation

A treatment performed to restore or enhance the productivity of a well. Stimulation treatments fall into two main groups, hydraulic fracturing treatments and matrix treatments. Fracturing treatments are performed above the fracture pressure of the reservoir formation and create a highly conductive flow path between the reservoir and the wellbore. Matrix treatments are performed below the reservoir fracture pressure and generally are designed to restore the natural permeability of the reservoir following damage to the near-wellbore area. Stimulation in shale gas reservoirs typically takes the form of hydraulic fracturing treatments.

dome

A type of anticline that is circular or elliptical rather than elongate. The upward migration of salt diapirs can form domes, called salt domes.

O ring

A type of circular seal commonly found in downhole tools and a wide range of surface equipment applications.

Organic deposits

A type of damage in which heavy hydrocarbons precipitate when temperature or pressure is reduced. These deposits are commonly located in the tubing, gravel pack and perforations, or inside the formation.

master valve

A valve located on the Christmas tree that controls all flow from the wellbore.

My

Abbreviation for million years apart from Ma.

Iron-oxidizing bacteria

Aerobic bacteria that convert iron from the ferrous [Fe+2] to the ferric [Fe+3] state and produce ferric hydroxide [Fe(OH)3], which is a highly insoluble by-product that will damage the formation.

Alkaline flooding or ASP

An EOR technique which generates a surfactant in-situ for displacing oil and is usually followed by polymer flooding for mobility control

TFNB

An abbreviation on drilling reports or mud logs signifying trip for new bit.

rod pump

An artificial-lift pumping system using a surface power source to drive a downhole pump assembly. A beam and crank assembly creates reciprocating motion in a sucker-rod string that connects to the downhole pump assembly. The pump contains a plunger and valve assembly to convert the reciprocating motion to vertical fluid movement.

Bell Nipple

An enlarged pipe at the top of a casing string that serves as a funnel to guide drilling tools into the top of a well.

washout

An enlarged region of a wellbore.

marsh

An environment from which water rarely drains that supports primarily grassy vegetation and does not form peat.

completion skin

An indicator used to determine the effect that key completion components have on the productionefficiency of a well. If one or more of the well-completion components create a localized pressure drop, the effect may be a reduction in the production capability of the well. Such conditions are evident as '''.

slimhole well

An inexact term describing a borehole (and associated casing program) significantly smaller than a standard approach, commonly a wellbore less than 6 in. in diameter.

Pig

Another name for a scraper.

Borehole

Another name to the wellbore itself, including the openhole or uncased portion of the well. It may refer to the inside diameter of the wellbore wall, the rock face that bounds the drilled hole.

The flocculation of asphaltene particles from reservoir fluid.

Asphaltene precipitation

syncline

Basin- or trough-shaped fold in rock in which rock layers are downwardly convex. The youngest rock layers form the core of the fold and outward from the core progressively older rocks occur. Synclines typically do not trap hydrocarbons because fluids tend to leak up the limbs of the fold. An anticline is the opposite type of fold, having upwardly-convex layers with old rocks in the core.

consolidation

Compaction and cementation of sediments to the degree that they become coherent, relatively solid rock. Typical consequences of consolidation include an increase in density and acoustic velocity, and a decrease in porosity.

sour corrosion

Corrosion associated with the presence of hydrogen sulfide [H2S].'' ''occurs in several forms of hydrogen embrittlement that cause materials to fail at stress levels below their normal yield strength.

sweet crude

Crude oil containing low levels of sulfur compounds, especially hydrogen sulfide [H2S]. The facilities and equipment to handle this crude are significantly simpler than those required for other potentially corrosive types of crude oil.

Capillary desaturation curves

Curve that plots residual saturations as a function of capillary number.

neritic

Describing the environment and conditions of the marine zone between low tide and the edge of the continental shelf, a depth of roughly 200 m [656 ft]. A neritic environment supports marine organisms, also described as neritic, that are capable of surviving in shallow water with moderate exposure to sunlight.

anomalous

Different from what is typical or expected, or different from what is predicted by a theoretical model. The difference or anomaly may refer to the measurement of the difference between an observed or measured value and the expected values of a physical property. Anomalies can be of great interest in hydrocarbon and mineral exploration because they often indicate hydrocarbon and mineral prospects and accumulations, such as geologic structures like folds and faults. Geochemical anomalies at the surface of the Earth can also indicate an accumulation of hydrocarbons at depth. Geophysical anomalies, such as amplitude anomalies in seismic data and magnetic anomalies in the Earth's crust, can also be associated with hydrocarbon accumulations.

Scraper trap

Equipment placed in a pipeline for inserting or retrieving a pipeline scraper.

clay

Fine-grained sediments less than 0.0039 mm in size.

trip gas (TG)

Gas entrained in the drilling fluid during a pipe trip, which typically results in a significant increase in gas that is circulated to surface. This increase arises from a combination of two factors: lack of circulation when the mud pumps are turned off, and swabbing effects caused by pulling the drillstring to surface. These effects may be seen following a short trip into casing or a full trip to surface.

tight gas

Gas produced from a relatively impermeable reservoir rock. Hydrocarbon production from tight reservoirs can be difficult without stimulation operations. Stimulation of tight formations can result in increased production from formations that previously might have been abandoned or been produced uneconomically. The term is generally used for reservoirs other than shales.

gas in solution

Gas that is dissolved in a liquid, such as water or oil.

petroleum system

Geologic components and processes necessary to generate and store hydrocarbons, including a mature source rock, migration pathway, reservoir rock, trap and seal. Appropriate relative timing of formation of these elements and the processes of generation, migration and accumulation are necessary for hydrocarbons to accumulate and be preserved. The components and critical timing relationships of a petroleum system can be displayed in a chart that shows geologic time along the horizontal axis and the petroleum system elements along the vertical axis. Exploration plays and prospects are typically developed in basins or regions in which a complete petroleum system has some likelihood of existing.

Sensitivity

In matrix stimulation, a characteristic of rock that indicates the degree of reaction between the rock minerals and a given treating fluid.

supply vessel

In offshore operations, any barge, boat or ship that brings materials and personnel to and from the rigsite.

reserve pit

In onshore operations, an earthen-bermed storage area for discarded drilling fluid.

core

Innermost layer of the Earth. Studies of compressional and shear waves indicate that the core makes up nearly 3500 km [2170 miles] of the Earth's radius of 6370 km [3950 miles]. Such studies also demonstrate that because shear waves do not pass through the outer part of the core (2250 km [1400 miles] thick), it is liquid (only solids can shear). The inner core is solid and 1220 km [750 miles] thick. The core's iron and nickel composition was inferred through studies of the Earth's gravitational field and average density. The relatively low density of the outer layers of the Earth suggests a dense inner layer.

strata

Layers of sedimentary rock.

tuff

Lithified volcanic ash.

density

Mass per unit of volume. Density is typically reported in g/cm3 (for example, rocks) or pounds per barrel (drilling mud) in the oil field.

Ma

Mega annum. The abbreviation for million years that is most commonly used in the geologic literature.

plankton

Minute organisms that float or drift passively near the surface of oceans and seas. Plant-like plankton, or phytoplankton, include diatoms. Zooplankton are animals that have a limited ability to move themselves. The changes in plankton over time are useful for estimation of relative ages of rocks that contain the fossilized remains of plankton.

Steam injection, In situ combustion

Name two methods of enhancing oil recovery via reduction of Oil viscosity and vaporization of light ends

derrickman

One of the rig crew members who gets his name from the fact that he works on a platform attached to the derrick or mast, typically 85 ft [26 m] above the rig floor, during trips.

pipe rack

Onshore, two elevated truss-like structures having triangular cross sections. It supports drillpipe, drill collars orcasing above the ground. These structures are used in pairs located about 20 ft [6 m] apart and keep the pipe above ground level and closer to the level of the catwalk. Offshore, the storage bins for drillpipe, drill collars and casing. The offshore version functions similarly to the onshore version.

benthos

Organisms that live at the bottom of a body of water.

Steam-oil ratio

Parameter used to monitor the efficiency of oil production processes based on steam injection. Commonly abbreviated as SOR, it measures the volume of steam required to produce one unit volume of oil.

plastic deformation

Permanent mechanical or physical alteration that does not include rupture. Plastic deformation of rocks typically occurs at high temperatures and pressures, conditions under which rocks become relatively viscous.

drilling crew

Personnel who operate the drilling rig. Typically consists of roustabouts, roughnecks, floor hands, lead tong operators, motormen, derrickmen, assistant drillers, and the driller.

terrestrial

Pertaining to sediments or depositional environments on land or above the level of high tide.

tectonism

Plate tectonic activity.

underpressure

Pore pressure less than normal or hydrostatic pressure. Underpressure, or a zone of underpressure, is common in areas or formations that have had hydrocarbon production.

vugular porosity

Pore space consisting of cavities or vugs. Vugular porosity can occur in rocks prone to dissolution, such as limestone, in which case it is secondary porosity.

underbalanced

Referring to a situation when the pressure (or force per unit area) exerted on a formation exposed in a wellbore is less than the internal fluid pressure of that formation. If sufficient porosity and permeability exist, formation fluids enter the wellbore. The drilling rate typically increases as an underbalanced condition is approached.

underpressured

Referring to pore pressure less than normal or hydrostatic pressure. Underpressure, or a zone of underpressure, is common in areas or formations that have had hydrocarbon production.

kelly down

Referring to the condition that occurs when the kelly is all the way down, so drilling progress cannot continue. A connectionmust be made, which has the effect of raising the kelly up by the length of the new joint of drillpipe added, so drilling can resume.

stuck

Referring to the varying degrees of inability to move or remove the drillstring from the wellbore.

vugular

Referring to vugs, which are cavities, voids or large pores in a rock that are commonly lined with mineral precipitates.

What does RCD stand for?

Rotating control device

clastic sediment

Sediment consisting of broken fragments derived from preexisting rocks and transported elsewhere and redeposited before forming another rock. Examples of common clastic sedimentary rocks include siliciclastic rocks such as conglomerate, sandstone, siltstone and shale. Carbonate rocks can also be broken and reworked to form clastic sedimentary rocks.

turbidite

Sedimentary deposits formed by turbidity currents in deep water at the base of the continental slope and on the abyssal plain. Turbidites commonly show predictable changes in bedding from coarse layers at the bottom to finer laminations at the top, known as Bouma sequences, that result from different settling velocities of the particle sizes present. The high energy associated with turbidite deposition can result in destruction of earlier deposited layers by subsequent turbidity currents.

deposit

Sediments that have accumulated, usually after being moved by wind, water or ice.

accommodation

Sequence stratigraphic term for the amount of space available for sediment accumulation. Dominant influences on the amount of accommodation, or accommodation space, include subsidence and eustasy.

siliciclastic sediment

Silica-based, noncarbonaceous sediments that are broken from preexisting rocks, transported elsewhere, and redeposited before forming another rock. Examples of common siliciclastic sedimentary rocks include conglomerate, sandstone, siltstone and shale. Carbonate rocks can also be broken and reworked to form other types of clastic sedimentary rocks.

Minimum miscibility pressure

Since the solvent miscibility should increase with pressure, the ultimate oil recovery should also increase.However, the oil recovery levels out and does not increase beyond a certain point. This pressure is know as ________

lost circulation material (LCM)

Solid material intentionally introduced into a mud system to reduce and eventually prevent the flow of drilling fluid into a weak, fractured or vugular formation. This material is generally fibrous or plate-like in nature, as suppliers attempt to design slurriesthat will efficiently bridge over and seal loss zones.

bedrock

Solid rock either exposed at the surface or situated below surface soil, unconsolidated sediments and weathered rock.

Dispersion

Spatial separation of components within a fluid. This separation is often driven by diffusion, mixing or differential flow.

casing

Steel pipe cemented in place during the construction process to stabilize the wellbore. The '' forms a major structural component of the wellbore and serves several important functions: preventing the formation wall from caving into the wellbore, isolating the different formations to prevent the flow orcrossflow of formation fluid, and providing a means of maintaining control of formation fluids and pressure as the well is drilled. The casing string provides a means of securing surface pressure control equipment and downholeproduction equipment, such as the drilling blowout preventer (BOP) orproduction packer. '' is available in a range of sizes and material grades.

clastic intrusion

Structures formed by sediment injection. Because they resemble intrusive and extrusive igneous features, much of the vocabulary for describing clastic intrusions, or injectites, comes from igneous geology. Sills are emplaced parallel to bedding, whereas dikes cut through bedding. The strata containing the intrusion are called host strata and the layers that feed the intrusion are the parent beds. Sand-injection features exhibit size scales from millimeters to kilometers, and have been seen in cores, borehole image logs, seismic sections, outcrops, aerial photographs and satellite images.

pore pressure gradient

The change in pore pressure per unit of depth, typically in units of psi/ft or kPa/m. Pressure increases predictably with depth in areas of normal pressure. The normal hydrostatic pressure gradient for freshwater is 0.433 psi/ft, or 9.792 kPa/m, and 0.465 psi/ft for water with 100,000 ppm total dissolved solids (a typical Gulf Coast water), or 10.516 kPa/m. Deviations from normal pressure are described as high or low pressure.

pressure gradient

The change in pressure per unit of depth, typically in units of psi/ft or kPa/m. Pressure increases predictably with depth in areas of normal pressure. The normal hydrostatic pressure gradient for freshwater is 0.433 psi/ft, or 9.792 kPa/m, and 0.465 psi/ft for water with 100,000 ppm total dissolved solids (a typical Gulf Coast water), or 10.516 kPa/m. Deviations from normal pressure are described as high or low pressure.

water coning

The change in the oil-water contact profile as a result of drawdown pressures during production. occurs in vertical or slightly deviated wells and is affected by the characteristics of the fluids involved and the ratio of horizontal to vertical permeability.

Cementer or Cementing Engineer

The colloquial term for the crew member in charge of a specialized cementing crew and trucks.

crossflow

The flow of fluid across the bottom of the bit after it exits the bit nozzles, strikes the bottom or sides of the hole and turns upwards to the annulus OR The flow of reservoir fluids from one zone to another

reverse circulation OR reversing out

The intentional pumping of wellbore fluids down the annulus and back up through the drillpipe. This is the opposite of the normal direction of fluid circulation in a wellbore.

toolpusher

The location supervisor for the drilling contractor. The toolpusher is usually a senior, experienced individual who has worked his way up through the ranks of the drilling crew positions.

pore pressure

The pressure of the subsurface formation fluids, commonly expressed as the density of fluid required in the wellbore to balance that pore pressure

Imbibition

The process of absorbing a wetting phase into a porous rock.

phase mobility

The ratio of the phase permeability to its viscosity

Mechanical efficiency

The ratio of the work done by an Artificial lift mechanism with respect to the energy input

rig floor

The relatively small work area in which the rig crew conducts operations, usually adding or removing drillpipe to or from the drillstring.

driller

The supervisor of the rig crew. He/she is responsible for the efficient operation of the rigsite as well as the safety of the crew and typically has many years of rigsite experience.

Travelling valve

The valve inside the SRP which goes down in the upstroke and up in the downstroke

Reservoir heterogeneities

The variations in rock properties in a reservoir.

make hole

To deepen a wellbore with the drill bit. To drill ahead.

blow down

To vent gas from a well or production system. Wells that have been shut in for a period frequently develop a gas cap caused by gas percolating through the fluid column in the wellbore. It is often desirable to remove or vent the free gas before starting well intervention work.

blowdown

To vent gas from a well or production system. Wells that have been shut in for a period frequently develop a gas cap caused by gas percolating through the fluid column in the wellbore. It is often desirable to remove or vent the free gas before starting well intervention work.

gravity toolface or high side toolface

Toolface angle used for deviated wells. Gravity toolface is the angle of the borehole survey instrument within the wellbore measured clockwise relative to up and in the plane perpendicular to the wellbore axis; the high side (maximum build), maximum right, low side (maximum drop) and maximum left directions have gravity toolface angles of 0°, 90°, 180° and 270°, respectively.

magnetic toolface

Toolface angle used for near-vertical wells. " "is the angle, or azimuth, of the borehole survey instrument within the wellbore measured clockwise relative to magnetic north and in the plane perpendicular to the wellbore axis; the north, east, south and west directions have magnetic toolface angles of 0°, 90°, 180° and 270°, respectively. Magnetic toolface may be corrected to reference either grid north or true north.

Tertiary recovery

Traditionally, the third stage of hydrocarbon production, comprising recovery methods that follow waterflooding or pressure maintenance.

brine

Water containing more dissolved inorganic salt than typical seawater.

Polymers used for polymer flooding

Xanthumgum, Polyacrylamide, Hydroxy ethylcellulose (HEC) and dextran polyethylene oxide (PEO) are examples or ?

pull out of hole

what does POOH stand for in drilling?

Capillary number

A dimensionless group used in analysis of fluid flow that characterizes the ratio of viscous forces to surface or interfacial tension forces.

Fingering

A condition whereby the interface of two fluids, such as oil and water, bypasses sections of reservoir as it moves along, creating an uneven, or fingered, profile. This is a relatively common condition in reservoirs with water-injection wells. The result is an inefficient sweeping action that can bypass significant volumes of recoverable oil and, in severe cases, an early breakthrough of water into adjacent production wellbores.

Ferrous sulfide

A corrosion by-product formed when hydrogen sulfide contacts the iron present in steel.

Breakthrough

A description of reservoir conditions under which a fluid, previously isolated or separated from production, gains access to a producing wellbore.

Cosurfactant

A chemical added to a process to enhance the effectiveness of a surfactant. Often used to increase the oil-solubilizing capacity of microemulsion surfactant systems.

Cosolvent

A chemical used in small quantities to improve the effectiveness of a primary solvent in a chemical process.

Disbonding

A common coating problem in which the protective coating detaches from the pipeline.

First-contact-miscibility

A condition of two fluids that are miscible that is, they form a single phase when mixed in any proportion when first brought into contact at a given pressure and temperature. In reservoir gasflooding, the injected gas composition, oil composition, temperature and the injection pressure determine the condition of first-contact miscibility.

Flow meter

A device for measuring in-situ the velocity of fluid flow in a well, usually one completed for production or injection.

Bond number

A dimensionless group used in analysis of fluid flow that characterizes the ratio of gravitational forces to surface or interfacial tension forces.

Emulsion

A dispersion of droplets of one liquid in another liquid with which it is incompletely miscible.

Flue gas

A gas generated by burning hydrocarbons with air; it is sometimes used as an enhanced oil recovery (EOR) injectant. The composition consists mainly of nitrogen, carbon dioxide, water vapor and excess oxygen with some impurities, such as carbon monoxide, nitrogen oxides and sulfur oxides.

Condensing drive

A gasflood process in which an injection gas enriched with components of intermediate molecular weight, for example butane, is injected into a reservoir to achieve multiple-contact miscibility. Upon contact with the oil, intermediate molecular-weight hydrocarbons transfer from the injected gas phase into the oil phase, a process in which those components are said to condense into the oil.

Chemical injection

A general term for injection processes that use special chemical solutions to improve oil recovery, remove formation damage, clean blocked perforations or formation layers, reduce or inhibit corrosion, upgrade crude oil, or address crude oil flow-assurance issues.

Chemical flooding

A general term for injection processes that use special chemical solutions.

Formation damage

A general term to describe the reduction in permeability to the near-wellbore area of a reservoir formation. A reduction in the natural capability of a reservoir to produce its fluids, such as a decrease in porosity or permeability, or both. Alteration of the far-field or virgin characteristics of a producing formation, usually by exposure to drilling fluids.

Backward multiple-contact test

A laboratory test to determine the phase envelope between oil and enriched gas. The test is conducted by equilibrating an oil sample several times with fresh samples of gas. Intermediate components are stripped from the gas by multiple contacts with the oil.

Constant composition expansion

A laboratory test usually performed as part of a routine PVT analysis that measures the change in volume of a reservoir fluid as a function of pressure.

Fire flooding

A method of thermal recovery in which a flame front is generated in the reservoir by igniting a fire at the sandface of an injection well. Continuous injection of air or other gas mixture with high oxygen content will maintain the flame front. As the fire burns, it moves through the reservoir toward production wells. Heat from the fire reduces oil viscosity and helps vaporize reservoir water to steam. The steam, hot water, combustion gas and a bank of distilled solvent all act to drive oil in front of the fire toward production wells.

Condensate

A natural gas liquid with a low vapor pressure compared with natural gasoline and liquefied petroleum gas. It is mainly composed of propane, butane, pentane and heavier hydrocarbon fractions. It is not only generated into the reservoir, but is also formed when liquid drops out, or condenses, from a gas stream in pipelines or surface facilities.

Critical matrix

A near-wellbore area where injected fluids such as acids can restore original permeability. Most of the reservoir pressure drop during production occurs in this near-wellbore part of the reservoir.

Cold heavy oil production with sand

A non-thermal primary process for producing heavy oil, also called CHOPS. In this method, continuous production of sand improves the recovery of heavy oil from the reservoir.

Electromagnetic heating

A process to increase thermal energy in a reservoir using electromagnetic means.

Cathodic protection

A technique used to minimize the rate of corrosion of a structure. It transfers corrosion from the structure under protection to a known location where artificial anodes (plates or metal bars) are placed and could be replaced easily. Used for floating vessels, platforms, storage tanks and pipelines

Corrosion fatigue

A type of corrosion in which the metal components of a structure fail due to cyclic stresses applied in a corrosive environment, such as salt water. Consequently, a break in the metal will occur at stresses considerably lower than the tensile strength of the material. This is the main cause of sucker-rod and drillstring failures.

Bimetallic corrosion

A type of corrosion in which two different metals are placed in contact in a corrosive environment. A small electric current flows from one piece of metal to the other, accelerating the corrosion rate of the more reactive of the two metals.

Erosion-corrosion

A type of corrosion produced when easily removed scales (such as iron carbonate) that were initially protecting the metals in the pipe are eroded and the underlying metals are corroded.

Clay swelling

A type of damage in which formation permeability is reduced because of the alteration of clay equilibrium. This occurs when water-based filtrates from drilling, completion, workover or stimulation fluids enter the formation. It can be caused by ion exchange or changes in salinity.

Dry forward combustion

A type of in situ combustion in which the burning front moves in the same direction as the injected air. As air is continuously supplied at the injection well, the fire ignited at this location moves toward the production wells.

Coating flaw

A void in the pipe coating.

Alkaline surfactant polymer... in relation to alkaline surfactant polymer flooding - an EOR method.

ASP stands for...

Eötvös number

Also called the bond number. A dimensionless group used in analysis of fluid flow that characterizes the ratio of gravitational forces to surface or interfacial tension forces.

Fluoboric acid

An acid mixture that generates more hydrofluoric [HF] acid as the HF is consumed. It can be used as a preflush, an overflush or as a main stage in a sandstone matrix acidizing.

Foaming agent

An additive used in preparation of foam used as a drilling fluid. These are usually nonionic surfactants and contain polymeric materials.

Foam flooding

An enhanced oil recovery process in which foam is injected into a reservoir to improve the sweep efficiency of a driving fluid. Foam can be generated either in the reservoir pore space or at the surface before injection.

Alkaline-flooding

An enhanced oil recovery technique in which chemicals react with certain types of oils, forming surfactants/petroleum soaps in-situ.

Equation of state

An equation that specifies fluid density as a function of pressure and temperature. A large body of scientific literature describes these functions for all kinds of hydrocarbons, and also for complex mixes of various hydrocarbons with other hydrocarbons and with other fluids.

Dry combustion

An in situ combustion technique in which only air or oxygen-enriched air mixtures are injected into a formation. A drawback related to this method is the highly corrosive and noxious combustion products that are produced.

Acetic acid

An organic acid used in oil and gas well-stimulation treatments. It is less corrosive than commonly used hydrochloric acid.

Dynamic miscibility

Another name for multi-contact miscibility. A dynamic fluid-mixing process in which an injected gas exchanges components with in situ oil until the phases achieve a state of miscibility within the mixing zone of the flood front.

Coating

Any thin material, liquid or powder, which, applied over a structure, forms a continuous film to protect against corrosion.

The minimum concentration of solvent injected into a reservoir oil at a given test pressure and temperature that causes asphaltene particles to precipitate from the oil.

Asphaltene onset concentration

As pressure decreases, the pressure at a given test temperature that first causes asphaltene to precipitate from a reservoir fluid.

Asphaltene onset pressure

Organic materials consisting of aromatic and naphthenic ring compounds containing nitrogen, sulfur and oxygen molecules. The organic part of the oil that is not soluble in straight-chain solvents such as pentane or heptane. Exist as a colloidal suspension stabilized by resin molecules in the oil.

Asphaltenes

API gravity = (141.5/0.82) - 131.5 =41.07

Calculation: An oil has a specific gravity of 0.82 at 60F. What is its API gravity?

Sweep efficiency

Define conformance

Volume of oil recovered/volume of oil contacted

Define displacement efficiency

Volume of oil contacted/volume of oil in place

Define sweep efficiency

A long-chain alcohol

Give an example of a possible cosurfactant

Corrosion inhibitor

In matrix treatments, a chemical added to acid that adsorbs on the pipe surface to form a protective film. This decreases the destructive reaction of acid with metals.

Preflush

Low salinity water injected prior to chemical flooding.

Damage

Natural or induced production impairments that can develop in the reservoir, the near-wellbore area, the perforations, the gravel-pack completion or the production pipelines, such as the tubing.

Ball sealer

Small spheres designed to seal perforations that are accepting the most fluid, thereby diverting reservoir treatments to other portions of the target zone.

Detergency

The ability of a chemical agent to remove a contaminant from a solid surface. For example, in enhanced oil recovery, a surfactant can be used to remove an oil phase from a mineral surface.

Contact angle

The angle of intersection of the interface between two fluids at a solid surface. The angle is measured from the solid surface through the aqueous phase, or in an oil and gas test through the oil phase. The angle displays hysteresis based on direction of motion of the interface.

Chemical potential

The change in the Gibbs free energy of a system when an infinitesimally small amount of a component is added under constant pressure and temperature while keeping the mass of the other components of the system unchanged.

Displacement front

The interface between an injectant and the fluid it is displacing.

Corrosion

The loss of metal due to chemical or electrochemical reactions, which could eventually destroy a structure.

Corrosion control

The measures used to prevent or considerably reduce the effects of corrosion.

Batch treatment

The pumping of a specific amount of treatment fluid, such as cement slurry, stimulation fluid, well completion fluid or chemical corrosion inhibitor.

Corrosion rate

The weight loss of a corrosion coupon after exposure to a corrosive environment, expressed as mils (thousandths of an inch) per year penetration.

API gravity = (141.5/SG at 60°F) - 131.5, where SG is the specific gravity of the fluid.

What is the formula for API gravity?

Alkaline chemicals such as sodium carbonate react with acidic oil components in-situ to create petroleum soap. In ASP flooding they prevent excessive adsorption of expensive manufactured surfactant.

What is the role of alkali in chemical EOR floods?

Smectite

Which clay suffers most often from clay swelling?

-Carbonate surfaces are positively charged - cannot use anionic surfactants and cationic surfactants are prohibitively expensive.

Why is Alkaline-surfactant-polymer flooding not recommended in carbonates?

-Abundance of calcium in carbonates - very bad precipitation occurs.

Why is alkali flooding not recommended for carbonate reservoirs?

Because it is counter to the behavior of pure substances, which vaporize when the pressure drops below the saturation pressure under isothermal conditions.

Why is condensate dissolution is called retrograde condensation?

Electrical double layer

With reference to formation evaluation, the layer between a clay particle and the formation water that has a particular distribution of ions.

Chelating agent

A chemical added to an acid to stabilize iron. The injected acid dissolves iron from rust, millscale, iron scales or iron-containing minerals in the formation.

Alkaline-surfactant-polymer flooding (ASP flooding)

A chemical enhanced oil recovery flood that uses two sources of surfactant and a polymer.

The surface is oil-wet.

A drop of oil is placed on a flat surface. The contact angle the droplet forms with the surface is much greater than 90 degrees. What can you conclude about the surface wettability?

Electrical coupon

Also called an electrical resistance probe. An instrument used in a corrosion testing to determine metal loss. The probe directly measures the increase in resistance of a metal as its cross-sectional area is reduced by corrosion. At suitable times, once the readings are obtained, these numbers are converted into corrosion rates

Coke

An insoluble organic deposit that has low hydrogen content. Also known as pyrobitumen, it is formed by thermal cracking and distillation during in-situ combustion.

Electrical resistance probe

An instrument used in a corrosion testing to determine metal loss. The probe directly measures the increase in resistance of a metal as its cross-sectional area is reduced by corrosion. At suitable times, once the readings are obtained, these numbers are converted into corrosion rates

Enhanced oil recovery

An oil recovery enhancement method using sophisticated techniques that alter the original properties of oil. Once ranked as a third stage of oil recovery that was carried out after secondary recovery, the techniques employed can actually be initiated at any time during the productive life of an oil reservoir. Its purpose is not only to restore formation pressure, but also to improve oil displacement or fluid flow in the reservoir.

Formic acid

An organic acid [HCOOH] used in oil- and gas-well stimulation treatments.

Compatability

In matrix stimulation, a characteristic of rock that indicates formation permeability is not reduced when treating fluids and their additives contact the formation minerals or fluids inside the reservoir. Especially important in sandstone treatments, in which potentially damaging reactions may occur.

Coating, oxygen scavenging, cathodic protection, chemical inhibition, chemical control

Give examples of corrosion control measures.

Polymer

Often used as a mobility buffer in chemical floods

Flooding pattern

The particular arrangement of production and injection wells. Common patterns are direct line drive, staggered line drive, two-spot, three-spot, four-spot, five-spot, seven-spot and nine-spot.

Displacement efficiency

The fraction of oil that has been recovered from a zone swept by a waterflood or other displacement process.

Flood front

The interface between an injectant and the fluid it is displacing.

Critical micelle concentration (CMC)

The surfactant concentration at which ordered aggregates of surfactant molecules known as micelles form and the the Gibbs Freen energy of the system is lowered.

Cold heavy oil production with sand

What does CHOPS stand for?

Critical micelle concentration (CMC)

What does CMC stand for?

Bicenter Bit

An integral bit and eccentric reamer used to simultaneously drill and underream the hole

collision

An interaction of lithospheric plates that can result in the formation of mountain belts and subduction zones. The collision of two plates of continental lithosphere, known as an A-type collision, can produce high mountains as rocks are folded, faulted and uplifted to accommodate the converging plates, as observed in the Alps and the Himalayas. B-type collisions, in which oceanic lithospheric plates collide with continental lithospheric plates, typically produce a subduction zone where the relatively denser oceanic plate descends below the relatively lighter continental plate, as seen on the Pacific coast of South America.

time and materials contract

An intermediate contract depth where the work to deepen the well would likely be done on a day rate basis

zone

An interval or unit of rock differentiated from surrounding rocks on the basis of its fossil content or other features, such as faults or fractures. For example, a fracture zone contains numerous fractures. A biostratigraphic zone contains a particular fossil or fossils.

dike

An intrusive rock that invades preexisting rocks, commonly in a tabular shape that cuts vertically or nearly vertically across preexisting layers. Dikes form from igneous and sedimentary rocks.

dyke

An intrusive rock that invades preexisting rocks, commonly in a tabular shape that cuts vertically or nearly vertically across preexisting layers. Dikes form from igneous and sedimentary rocks.

goose neck

An inverted "U" shaped section of rigid piping normally used as a conduit for high-pressure drilling fluid. In particular, the term is applied to a structure that connects the top of a vertical standpipe running up the side of a derrick or mast to a flexible kelly hose that in turn is connected to another one of these between the flexible line and the swivel.

jet OR jet mixer

1. A small-diameter tungsten carbide nozzle used in drill bits to produce a high-velocity drilling fluid stream exiting the bit.

pad

1. A temporary drilling site, usually constructed of local materials such as gravel, shell or even wood. For some long-drilling-duration, deep wells, the temporary drilling site may be paved with asphalt or concrete. After the drilling operation is over, most of the site is usually removed or plowed back into the ground.

drift

1. A term to describe the inclination from vertical of a wellbore.

lease

1. The act of acquiring acreage for exploration or production activity. 2. An area of surface land on which exploration or production activity occurs.

displacement

1. The shortest distance from the surface location of a well to the vertical projection of the bottom of the well (or other point in the well) to the Earth's surface.

Reasons for surface casing

1. The surface casing protects fresh-water aquifers onshore. 2. the surface casing provides minimal pressure integrity, and thus enables a diverter or perhaps even a blowout preventer (BOP) to be attached to the top of the surface casing string after it is successfully cemented in place. 3. the surface casing provides structural strength so that the remaining casing strings may be suspended at the top and inside of the surface casing.

closure

1. The vertical distance from the apex of a structure to the lowest structural contour that contains the structure. Measurements of both the areal closure and the distance from the apex to the lowest closing contour are typically incorporated in calculations of the estimated hydrocarbon content of a trap.

yield

1. The volume occupied by one sack of dry cement after mixing with water and additives to form a slurry of a desired density. Yield is commonly expressed in US units as cubic feet per sack (cu. ft./sk). 2. The specified minimum yield strength of steel used in pipe. For example, the yield of N-80 casing is 80,000 psi [552 MPa].

pack off

1. To plug the wellbore around a drillstring. This can happen for a variety of reasons, the most common being that either thedrilling fluid is not properly transporting cuttings and cavings out of the annulus or portions of the wellbore wall collapse around the drillstring.

spud

1. To start the well drilling process by removing rock, dirt and other sedimentary material with the drill bit.

mandrel

A bar, shaft or spindle around which other components are arranged or assembled. The term has been extended in oil and gas well terminology to include specialized tubular components that are key parts of an assembly or system, such as gas-lift mandrel or packer mandrel.

round thread

A basic threadform commonly found in oilfield applications. The thread profile of a '' ''' is designed to provide both mechanical strength and a hydraulic seal when made up to the correct torque.

conformity

A bedding surface separating younger from older strata, along which there is no evidence of subaerial or submarine erosion or of nondeposition, and along which there is no evidence of a significant hiatus. Unconformities (sequence boundaries) and flooding surfaces (parasequence boundaries) pass laterally into correlative conformities, or correlative surfaces.

Mixed deposits

A blend of organic and inorganic compounds such as scales, silts or clays. Migrating fines that become oil-wet often become targets for organic deposits, thereby creating this form of formation damage.

massif

A block of rock that forms a structural or topographic feature, such as a block of igneous of metamorphic rock within an area of mountain building, or orogeny. A massif can be as large as a mountain and is typically more rigid than the rocks that surround it.

outcrop

A body of rock exposed at the surface of the Earth. Construction of highways and other man-made facilities and resultant removal of soil and rock has created spectacular outcrops in some regions.

aquifer

A body of rock whose fluid saturation, porosity and permeability permit production of groundwater. A water-bearing portion of a petroleum reservoir with a waterdrive.

active margin

A boundary of colliding lithospheric plates. The present subduction zones of the Pacific Rim, the older mountains of the Alps, and the Himalayas represent active margins.

gas oil contact

A bounding surface in a reservoir above which predominantly gas occurs and below which predominantly oil occurs. Gas and oil are miscible, so the contact between gas and oil is transitional, forming a zone containing a mix of gas and oil.

gas water contact

A bounding surface in a reservoir above which predominantly gas occurs and below which predominantly water occurs. Gas and water are somewhat miscible, so the contact between gas and water is not necessarily sharp and there is typically a transition zone between 100% gas and 100% water in reservoirs.

oil water contact

A bounding surface in a reservoir above which predominantly oil occurs and below which predominantly water occurs. Although oil and water are immiscible, the contact between oil and water is commonly a transition zone and there is usually irreducible water adsorbed by the grains in the rock and immovable oil that cannot be produced. The oil-water contact is not always a flat horizontal surface, but instead might be tilted or irregular.

fault

A break or planar surface in brittle rock across which there is observable displacement. Depending on the relative direction of displacement between the rocks, or fault blocks, on either side of the fault, its movement is described as normal, reverse or strike-slip. According to terminology derived from the mining industry, the fault block above the fault surface is called the hanging wall, while the fault block below the fault is the footwall. Given the geological complexity of some faulted rocks and rocks that have undergone more than one episode of deformation, it can be difficult to distinguish between the various types of faults. Also, areas deformed more than once or that have undergone continual deformation might have fault surfaces that are rotated from their original orientations, so interpretation is not straightforward. In a normal fault, the hanging wall moves down relative to the footwall along the dip of the fault surface, which is steep, from 45o to 90o. A growth fault is a type of normal fault that forms during sedimentation and typically has thicker strata on the downthrown hanging wall than the footwall. A reverse fault forms when the hanging wall moves up relative to the footwall parallel to the dip of the fault surface. A thrust fault, sometimes called an overthrust, is a reverse fault in which the fault plane has a shallow dip, typically much less than 45o. Movement of normal and reverse faults can also be oblique as opposed to purely parallel to the dip direction of the fault plane. The motion along a strike-slip fault, also known as a transcurrent or wrench fault, is parallel to the strike of the fault surface, and the fault blocks move sideways past each other. The fault surfaces of strike-slip faults are usually nearly vertical. A strike-slip fault in which the block across the fault moves to the right is described as a dextral strike-slip fault. If it moves left, the relative motion is described as sinistral. A transform fault is a particular type of strike-slip fault that is a boundary of an oceanic tectonic plate. The actual movement of a transform fault is opposite to its apparent displacement. The presence of a fault can be detected by observing characteristics of rocks such as changes in lithology from one fault block to the next, breaks and offsets between strata or seismic events, and changes in formation pressure in wells that penetrate both sides of a fault. Some fault surfaces contain relatively coarse rubble that can act as a conduit for migrating oil or gas, whereas the surfaces of other faults are smeared with impermeable clays or broken grains that can act as a fault seal.

connection gas

A brief influx of gas that is introduced into the drilling fluid when a pipe connection is made.

connection gas

A brief influx of gas that is introduced into the drilling fluid when a pipe connection is made. Before making a connection, the driller stops the mud pumps, thereby allowing gas to enter the wellbore at depth. Gas may also be drawn into the wellbore by minor swabbing effects resulting from short movements of the drillstring that occur during the connection. Usually occurs after one lag interval following the connection. On a mud log, it will appear as a short peak above background levels. This peak often appears at 30-foot intervals, depending on the lengths of drillpipe being connected as the well is drilled.

scout ticket

A brief report about a well from the time it is permitted through drilling and completion. This typically includes the location, total depth, logs run, production status and formation tops.

fluid-loss additive

A chemical additive used to control the loss of fluid to the formation through filtration. In cementingoperations, loss of the aqueous phase can severely affect the performance of the slurry and set cement. In almost any operation, loss of fluid to the reservoir formation carries a high risk of permeability damage

coal

A carbon-rich sedimentary rock that forms from the remains of plants deposited as peat in swampy environments. Burial and increase in temperature bring about physical and chemical changes called coalification. Because of the organic origin of coal, it cannot be classified as a mineral. The main types of coal, anthracite, bituminous coal and lignite, can be distinguished by their hardness and energy content, which are affected by their organic content as well as their conditions of formation. Natural gas associated with coal, called coal gas or coalbed methane, can be produced economically from coal beds in some areas. In some basins coals form source rocks.

limestone

A carbonate sedimentary rock predominantly composed of calcite of organic, chemical or detrital origin. Minor amounts of dolomite, chert and clay are common in limestones. Chalk is a form of fine-grained limestone.

liner

A casing string that does not extend to the top of the wellbore, but instead is anchored or suspended from inside the bottom of the previous casing string. There is no difference between the casing joints themselves.

intermediate casing

A casing string that is generally set in place after the surface casing and before the production casing. The ''' '''' string provides protection against caving of weak or abnormally pressured formations and enables the use of drilling fluids of different density necessary for the control of lower formations.

production casing

A casing string that is set across the reservoir interval and within which the primary completion components are installed.

hydrothermal alteration

A change of preexisting rocks or minerals caused by the activity of hot solutions, such as fluids accompanying or heated by magma. Quartz, serpentine and chlorite are minerals commonly associated with hydrothermal alteration. Ore deposits, such as lead (as the mineral galena), zinc (sphalerite), and copper (malachite), can occur in areas of hydrothermal alteration.

Bouma sequence

A characteristic sequence of sedimentary structures occurring in sedimentary rocks deposited in areas of deep water sedimentation by turbidity currents, which form deposits called turbidites. In theory, a complete Bouma sequence comprises sediments that fine upwards, consisting of a lowermost layer of coarse, chaotic clastic sediments deposited under conditions of high depositional energy overlain by successively finer grained and better stratified sediments like sands and muds deposited under calmer conditions that are labeled as Units A though E. In practice, however, the chaotic, high-energy nature of turbidite deposition can alter or remove underlying sediments so that incomplete sequences of sediments typically remain preserved.

thread protector

A cheap, expendable, perhaps even disposable threaded shape to mate with threads on drillstring and casing components. Thread protectors prevent harmful impacts and other contact to the metal thread surfaces. Some protectors are strong enough and are fitted with lifting eyes so that they may be screwed into a joint of drillpipe, a drill collar or another component and a chain tied to the eye for lifting the joint. Except for this type, most of the other available styles of thread protectors are relatively inexpensive, being made from thermoplastics and various epoxy resins.

Flapper Valve

A check valve that has a spring-loaded plate that may be pumped through, generally in the downhole direction, but closes if the fluid attempts to flow back through the drillstring to the surface.

flapper valve

A check valve that has a spring-loaded plate that may be pumped through, generally in the downhole direction, but closes if the fluid attempts to flow back through the drillstring to the surface.

Reducing agent

A chemical added to an acid to stabilize iron. The injected acid dissolves iron from rust, millscale, iron scales or iron-containing minerals in the formation.

chelating agent

A chemical added to an acid to stabilize iron. The injected acid dissolves iron from rust, millscale, iron scales or iron-containing minerals in the formation. Iron can exist as ferric iron [Fe+3] or ferrous iron [Fe+2]. If the iron is not controlled, it will precipitate insoluble products such as ferric hydroxide and, insour environments, ferrous sulfide [FeS], which will damage the formation.

cement accelerator

A chemical additive mixed with cement slurry to reduce the time required for the set cement to develop sufficient compressive strength to enable drilling operations to continue. ''' are generally used in near-surface applications in which the temperature is relatively low.

cement extender

A chemical additive or inert material used to decrease the density or increase the yield of a cementslurry. The slurry yield is typically expressed in cubic feet of slurry per sack of cement. Increasing the yield reduces the cost per volume of cement slurry, while reducing the slurry density reduces thehydrostatic pressure of the cement column, enabling weak zones to be successfully cemented and isolated.

cement dispersant

A chemical additive that reduces the cement slurry viscosity to improve fluid flow characteristics. Adequately dispersed cement slurries exhibit improved fluid-loss control, can displace drilling fluid more efficiently and be successfully mixed and pumped at higher densities.

retarder

A chemical additive used to increase the thickening time of cement slurries or similar fluids that may have a limited pumping time. The increased pressure and temperature typically associated with deep wellbores requires the use of such performance-enhancing additives to enable efficient placement without premature setting.

inhibitor

A chemical agent added to a fluid system to retard or prevent an undesirable reaction that occurs within the fluid or with the materials present in the surrounding environment

diverter

A chemical agent or mechanical device used in injection treatments, such as matrix stimulation, to ensure a uniform distribution of treatment fluid across the treatment interval. Injected fluids tend to follow the path of least resistance, possibly resulting in the least permeable areas receiving inadequate treatment. By using some means of diversion, the treatment can be focused on the areas requiring the most treatment. To be effective, the diversion effect should be temporary to enable the full productivity of the well to be restored when the treatment is complete.

chemical diverter

A chemical agent used in stimulation treatments to ensure uniform injection over the area to be treated. ''' function by creating a temporary blocking effect that is safely cleaned up following the treatment, enabling enhanced productivity throughout the treated interval.

diverting agent

A chemical agent used in stimulation treatments to ensure uniform injection over the area to be treated.'''', also known as chemical diverters, function by creating a temporary blocking effect that is safely cleaned up following the treatment, enabling enhanced productivity throughout the treated interval.

cement retarder

A chemical agent used to increase the thickening time of cement slurries to enable proper placement. The need for ''' increases with depth due to the greater time required to complete thecementing operation and the effect of increased temperature on the cement-setting process.

Surfactant

A chemical that preferentially adsorbs at an interface, lowering the surface tension or interfacial tension between fluids or between a fluid and a solid. This term encompasses a multitude of materials that function as emulsifiers, dispersants, oil-wetters, water-wetters, foamers and defoamers.

scale inhibitor

A chemical treatment used to control or prevent scale deposition in the production conduit or completionsystem. '' '' chemicals may be continuously injected through a downhole injection point in the completion, or periodic squeeze treatments may be undertaken to place the inhibitor in the reservoirmatrix for subsequent commingling with produced fluids.

Sequestering agent

A chemical whose molecular structure can envelop and hold a certain type of ion in a stable and soluble complex.

silica

A chemically resistant dioxide of silicon that occurs in crystalline (quartz), amorphous (opal) and cryptocrystalline (chert) forms.

geologic time scale

A chronological chart of the stages and ages of events in the history of the Earth, from its initial formation to present, that has been constructed on the basis of the rock record. As is the typical natural position of rocks, the oldest event is at the bottom of the chart and the youngest is at the top. Both absolute and relative ages of rocks and fossils supplement interpretations from rocks. The vastness of geologic time and the slowness of geological processes are difficult to capture in a simple chart.

evaporite

A class of sedimentary minerals and sedimentary rocks that form by precipitation from evaporating aqueous fluid. Common evaporite minerals are halite, gypsum and anhydrite, which can form as seawater evaporates, and the rocks limestone and dolostone. Certain evaporite minerals, particularly halite, can form excellent cap rocks or seals for hydrocarbon traps because they have minimal porosity and they tend to deform plastically (as opposed to brittle fracturing that would facilitate leakage).

carbonate (noun)

A class of sedimentary rock whose chief mineral constituents (95% or more) are calcite and aragonite (both CaCo3) and dolomite [CaMg(CO3)2], a mineral that can replace calcite during the process of dolomitization. Limestone, dolostone or dolomite, and chalk are carbonate rocks. Although carbonate rocks can be clastic in origin, they are more commonly formed through processes of precipitation or the activity of organisms such as coral and algae. Carbonates form in shallow and deep marine settings, evaporitic basins, lakes and windy deserts. Carbonate rocks can serve as hydrocarbon reservoir rocks, particularly if their porosity has been enhanced through dissolution. They rely on fractures for permeability.

sandstone

A clastic sedimentary rock whose grains are predominantly sand-sized. The term is commonly used to imply consolidated sand or a rock made of predominantly quartz sand, although sandstones often contain feldspar, rock fragments, mica and numerous additional mineral grains held together with silica or another type of cement. The relatively high porosity and permeability of sandstones make them good reservoir rocks.

cathead

A clutched spool connected to the drawworks power system used to tension chains, cables and softlinerope.

makeup cathead

A clutched, rotating spool that enables the driller to use the drawworks motor to apply tension to a chain connected to themakeup tongs. This tensioned chain, acting at right angles to the tong handle, imparts torque to the connection being tightened.

Breakout Cathead

A clutching mechanism that permits the driller to apply high torque to a connection using the power of the drawworks motor.

granite

A coarse-grained, plutonic or intrusive igneous rock of felsic composition having large crystals of quartz, feldspar and mica. In the oil field, "granite" is sometimes used incorrectly to indicate any type of hard rock.

nitrogen cushion

A column of high-pressure nitrogen typically applied to a tubing string in preparation for drillstem testing or perforating operations in which the reservoir formation is to be opened to the tubing string.

gamma ray log

A common and inexpensive measurement of the natural emission of gamma rays by a formation. They are particularly helpful because shales and sandstones typically have different gamma ray signatures that can be correlated readily between wells.

carbonate scale

A common type of mineral deposit that is often found on wellbore tubulars and components as thesaturation of produced water is affected by changing temperature and pressure conditions in theproduction conduit. ''' have a high dissolution rate in common oilfield acids and generally can be effectively removed using acid or chemical treatments. Scale inhibition techniques also may be used to prevent scale formation. In the majority of cases, scale prevention is simpler and more cost-effective than attempting a cure.

Scale removal

A common well-intervention operation involving a wide variety of mechanical and chemical treatment options.

survey

A completed measurement of the inclination and azimuth of a location in a well (typically the total depth at the time of measurement).

deviation survey OR directional survey

A completed measurement of the inclination and azimuth of a location in a well (typically the total depthat the time of measurement).

slip joint

A completion component designed to accommodate tubing movement or length changes while maintaining a hydraulic seal between the production conduit and the annulus.

landing nipple

A completion component fabricated as a short section of heavy wall tubular with a machined internal surface that provides a seal area and a locking profile.

nipple

A completion component fabricated as a short section of heavy wall tubular with a machined internal surface that provides a seal area and a locking profile.

seating nipple

A completion component fabricated as a short section of heavy wall tubular with a machined internal surface that provides a seal area and a locking profile. Landing nipples are included in most completions at predetermined intervals to enable the installation of flow-control devices, such as plugs and chokes.

side pocket mandrel

A completion component that is used to house gas-lift valves and similar devices that require communication with the annulus. The design of this device is such that the installed components do not obstruct the production flow path, enabling access to the wellbore and completion components below.

circulation device

A completion component, generally included in the lower assembly near the packer, that allows communication between the tubing and annulus. ''' enable the circulation of fluids forwell control or kickoff purposes.

casing completion

A completion configuration in which a production casing string is set across thereservoir interval and perforated to allow communication between theformation and wellbore. The casing performs several functions, including supporting the surrounding formation under production conditions, enabling control of fluid production through selective perforation and allowing subsequent or remedial isolation by packers, plugs or special treatments.

tubingless completion

A completion design in which the reservoir fluids are produced through small-diameter casing. The absence of a separate tubing string significantly limits the operating and contingency options available for the well.

sliding sleeve

A completion device that can be operated to provide a flow path between the production conduit and theannulus. incorporate a system of ports that can be opened or closed by a sliding component that is generally controlled and operated by slickline tool string.

filtered brine

A completion or workover fluid that has been treated to remove debris and fine particles that may cause near-wellbore damage if allowed to enter the reservoir formation.

natural completion

A completion system designed to utilize the natural flow capability of the reservoir.

coiled tubing completion

A completion that utilizes coiled tubing as the production conduit, or as a means of conveying and installing completion equipment or components. Since the coiled tubing string is continuous, problems associated with connections are avoided. Also, the pressure-control equipment used on coiled tubing operations enables work to be safely conducted on live wells.

petroleum

A complex mixture of naturally occurring hydrocarbon compounds found in rock. Petroleum can range from solid to gas, but the term is generally used to refer to liquid crude oil. Impurities such as sulfur, oxygen and nitrogen are common in petroleum. There is considerable variation in color, gravity, odor, sulfur content and viscosity in petroleum from different areas.

float collar

A component installed near the bottom of the casing string on which cementplugs land during the primary cementing operation. It typically consists of a short length of casing fitted with a check valve. This device may be a flapper-valve type, a spring-loaded ball valve or other type.

landing collar

A component installed near the bottom of the casing string on which thecement plugs land during the primary cementing operation.

drill collar

A component of a drillstring that provides weight on bit for drilling. They are thick-walled tubular pieces machined from solid bars of steel, usually plain carbon steel but sometimes of nonmagnetic nickel-copper alloy or other nonmagnetic premium alloys. The bars of steel are drilled from end to end to provide a passage to pumping drilling fluids through the collars.

exploration play

A conceptual model for a style of hydrocarbon accumulation used by explorationists to develop prospects in a basin, region or trend and used by development personnel to continue exploiting a given trend. A play (or a group of interrelated plays) generally occurs in a single petroleum system.

Mobility control

A condition in oil recovery processes whereby the mobility of the injectant is lower than that of the oil or preceding chemical slug, leading to a stable displacement by the injectant.

Gas lock

A condition sometimes encountered in a pumping well when dissolved gas, released from solution during the upstroke of the plunger, appears as free gas between the valves. On the downstroke, pressure inside a barrel completely filled with gas may never reach the pressure needed to open the traveling valve. In the upstroke, the pressure inside the barrel never decreases enough for the standing valve to open and allow liquid to enter the pump. Thus no fluid enters or leaves the pump, and the pump is locked. It does not cause equipment failure, but with a nonfunctional pump, the pumping system is useless. A decrease in pumping rate is accompanied by an increase of bottomhole pressure (or fluid level in the annulus). In many cases of _______, this increase in bottomhole pressure can exceed the pressure in the barrel and liquid can enter through the standing valve. After a few strokes, enough liquid enters the pump that the ________ in broken, and the pump functions normally.

screen out

A condition that occurs when the solids carried in a treatment fluid, such as proppant in a fracture fluid, create a bridge across the perforations or similar restricted flow area. This creates a sudden and significant restriction to fluid flow that causes a rapid rise in pump pressure.

differential pressure sticking OR differential sticking OR wall sticking

A condition whereby the drillstring cannot be moved (rotated or reciprocated) along the axis of the wellbore.Typically occurs when high-contact forces caused by low reservoir pressures, high wellbore pressures, or both, are exerted over a sufficiently large area of the drillstring. This is, for most drilling organizations, the greatest drilling problem worldwide in terms of time and financial cost.

trap

A configuration of rocks suitable for containing hydrocarbons and sealed by a relatively impermeable formation through which hydrocarbons will not migrate. Traps are described as structural traps (in deformed strata such as folds and faults) or stratigraphic traps (in areas where rock types change, such as unconformities, pinch-outs and reefs). A trap is an essential component of a petroleum system.

correlation

A connection of points from well to well in which the data suggest that the points were deposited at the same time (chronostratigraphic) or have similar and related characteristics.

flange

A connection profile used in pipe work and associated equipment to provide a means of assembling and disassembling components. Most oilfield '''' feature a bolt-hole pattern to allow the joint to be secured and a gasket profile to ensure a pressure-tight seal. The design and specification of a ''' relates to the size and pressure capacity of the equipment to which it is fitted.

Bit Box

A container, usually made of steel and fitted with a sturdy lock, to store drill bits, especially higher cost PDC and diamond bits

isochore

A contour connecting points of equal true vertical thickness of strata, formations, reservoirs or other rock units. A map that displays isochores is an isochore map. The terms isopach and isopach map are incorrectly used interchangeably to describe isochores and isochore maps. Isopachs and isochores are equivalent only if the rock layer is horizontal.

topographic map

A contour map that displays the elevation of the Earth's surface. This map is commonly used as the base map for surface geological mapping.

isopach

A contour that connects points of equal thickness. Commonly, the isopachs, or contours that make up an isopach map, display the stratigraphic thickness of a rock unit as opposed to the true vertical thickness. Isopachs are true stratigraphic thicknesses; i.e., perpendicular to bedding surfaces.

natural fracture

A crack or surface of breakage within rock not related to foliation or cleavage in metamorphic rock along which there has been no movement. A fracture along which there has been displacement is a fault. When walls of a fracture have moved only normal to each other, the fracture is called a joint. Fractures can enhance permeability of rocks greatly by connecting pores together, and for that reason, fractures are induced mechanically in some reservoirs in order to boost hydrocarbon flow. Fractures may also be referred to as natural fractures to distinguish them from fractures induced as part of a reservoir stimulation or drilling operation. In some shale reservoirs, natural fractures improve production by enhancing effective permeability. In other cases, natural fractures can complicate reservoir stimulation.

caliche

A crust of coarse sediments or weathered soil rich in calcium carbonate. It forms when lime-rich groundwater rises to the surface by capillary action and evaporates into a crumbly powder, forming a tough, indurated sheet called calcrete. Caliche typically occurs in desert or semi-arid areas. Of particular concern to geophysicists is the difficulty in acquiring good seismic data when shooting through a layer of caliche. A deposit of sodium nitrate that is mined and used for fertilizer in parts of South America.

mineral

A crystalline substance that is naturally occurring, inorganic, and has a unique or limited range of chemical compositions. These are homogeneous, having a definite atomic structure. Rocks are composed of These, except for rare exceptions like coal, which is a rock but not a mineral because of its organic origin. Minerals are distinguished from one another by careful observation or measurement of physical properties such as density, crystal form, cleavage (tendency to break along specific surfaces because of atomic structure), fracture (appearance of broken surfaces), hardness, luster and color. Magnetism, taste and smell are useful ways to identify only a few minerals.

storm packer

A heavy-duty retrievable packer assembly that can be run in to isolate the wellbore of a new well in the event of suspended activities, for example, during a severe storm.

sedimentary basin

A depression in the crust of the Earth formed by plate tectonic activity in which sediments accumulate. Continued deposition can cause further depression or subsidence. Sedimentary basins, or simply basins, vary from bowl-shaped to elongated troughs. If rich hydrocarbon source rocks occur in combination with appropriate depth and duration of burial, hydrocarbon generation can occur within the basin.

basin

A depression in the crust of the Earth, caused by plate tectonic activity and subsidence, in which sediments accumulate. Sedimentary basins vary from bowl-shaped to elongated troughs. Basins can be bounded by faults. Rift basins are commonly symmetrical; basins along continental margins tend to be asymmetrical. If rich hydrocarbon source rocks occur in combination with appropriate depth and duration of burial, then a petroleum system can develop within the basin. Most basins contain some amount of shale, thus providing opportunities for shale gas exploration and production.

breakthrough

A description of reservoir conditions under which a fluid, previously isolated or separated fromproduction, gains access to a producing wellbore. The term is most commonly applied to water or gas '''', where the water or gas injected to maintain reservoir pressure via injection wells breaks through to one or more of the producing wells.

fullbore

A description of the internal area and surfaces of a tool or tubular assembly through which there is an unimpeded internal diameter. In some cases, ''' is used to describe the form of a nominal internal diameter that extends over the length of the tool or interval without any variation. In other applications, the term simply implies an ability to pass a ball or similar item of a stated drift diameter through the assembly.

tubing hanger

A device attached to the topmost tubing joint in the wellhead to support the tubing string.

blasting cap

A device containing primary high-explosive material that is used to initiate an explosive sequence. The two common types of detonators are electrical detonators (also known as blasting caps) and percussion detonators. Electrical detonators have a fuse material that burns when high voltage is applied to initiate the primary high explosive. Percussion detonators contain abrasive grit and primary high explosive in a sealed container that is activated by a firing pin. The impact force of the firing pin is sufficient to initiate the ballistic sequence that is then transmitted to the detonating cord. Several safety systems are used in conjunction with detonators to avoid accidental firing during rig-up or rig-down. Safety systems also are used to disarm the gun or ballistic assembly if downhole conditions are unsafe for firing.

Cement Head

A device fitted to the top joint of a casing string to hold a cement plug before it is pumped down the casing during the cementing operation

cement head

A device fitted to the top joint of a casing string to hold a cement plug before it is pumped down the casing during the cementing operation. In most operations, a bottom plug is launched before thespacer or cement slurry. The top plug is released from the cement head after the spacer fluid.

centralizer

A device fitted with a hinged collar and bowsprings to keep the casing or linerin the center of the wellbore to help ensure efficient placement of a cementsheath around the casing string. If casing strings are cemented off-center, there is a high risk that a channel of drilling fluid or contaminated cement will be left where the casing contacts the formation, creating an imperfect seal.

scratcher

A device for cleaning mud and mud filter cake off of the wellbore wall when cementing casing in the hole to ensure good contact and bonding between the cement and the wellbore wall.

choke

A device incorporating an orifice that is used to control fluid flow rate or downstream system pressure. ''' are available in several configurations for both fixed and adjustable modes of operation. Adjustable '' enable the fluid flow and pressure parameters to be changed to suit process orproduction requirements. Fixed ''' do not provide this flexibility, although they are more resistant toerosion under prolonged operation or production of abrasive fluids.

expansion joint

A device or completion component designed to enable relative movement between two fixed assemblies in the event of thermal expansion or contraction. The forces generated by thermal expansion or contraction can be significant. '''' '''' within the completion assembly prevent any movement or forces being transmitted to fixed components such as packers or tubing hangers.

ram blowout preventer

A device that can be used to quickly seal the top of the well in the event of a well control event (kick). It consists of two halves of a cover for the well that are split down the middle. Large-diameter hydraulic cylinders, normally retracted, force the two halves of the cover together in the middle to seal the wellbore.

equalizing valve

A device that is operated to equalize the pressure across a valve, plug or similar pressure or fluid isolation barrier. The operating mechanism on many pressure-sealing devices is rendered inoperable once the mechanism has been activated by pressure. In such cases, the pressure across the pressure barrier must be equalized before the barrier can be removed.

degasser

A device that removes air or gases (methane, H2S, CO2 and others) from drilling liquids. There are two generic types that work by both expanding the size of the gas bubbles entrained in the mud (by pulling a vacuum on the mud) and by increasing the surface area available to the mud so that bubbles escape (through the use of various cascading baffle plates)

top drive

A device that turns the drillstring. It consists of one or more motors (electric or hydraulic) connected with appropriate gearing to a short section of pipe called a quill, that in turn may be screwed into a saver sub or the drillstring itself.

screen

A device used in sand control applications to support the gravel pack. To form a screen, a profiled wire is wrapped and welded in place on a perforated liner. '' are available in a range of sizes and specifications, including outside diameter, material type and the geometry and dimension of the screen slots. The space between each wire wrap must be small enough to retain the gravel placed behind, yet minimize any restriction to production.

opening bomb

A device used in stage cementing to open the stage collar or diverting valve through which the second or subsequent cement stage is placed.

liner hanger

A device used to attach or hang liners from the internal wall of a previous casing string.

packing gland

A device used to seal around a reciprocating or rotating shaft or spindle. A malleable packing compound is forced into place by an adjustable packing nut, or similar arrangement. This enables the seal or packing to be tightened to suit the operating conditions and allows subsequent adjustment to account for wear.

gas separator

A device used to separate entrained gas from production liquids. Surface processing facilities generally use '' ''' to render the liquids safe for further processing or disposal. '' ''' equipment is also used in downhole applications, such as the protection of pumping equipment against gas lock by separating and redirecting free gas at the pump suction or inlet.

skin

A dimensionless factor calculated to determine the production efficiency of a well by comparing actual conditions with theoretical or ideal conditions. A positive value indicates some damage or influences that are impairing well productivity. A negative value indicates enhanced productivity, typically resulting from stimulation.

pore

A discrete void within a rock, which can contain air, water, hydrocarbons or other fluids. In a body of rock, the percentage of pore space is the porosity.

Winsor phase behavior

A distinction among three phase behaviors of oil, water and surfactant systems when they form a microemulsion

injection mandrel

A downhole completion component that enables injection of treatment chemicals or inhibitors into theproduction conduit.

ball catcher

A downhole device or assembly used to catch and retain balls used to actuate ball-operated tools or equipment. Following activation, some ball-operated tools incorporate a means of ejecting the activation ball to regain a fullbore flow path. In such cases, the ball can be retained in a '''

downhole safety valve (DSV)

A downhole device that isolates wellbore pressure and fluids in the event of an emergency or catastrophic failure of surface equipment. The control systems associated with safety valves are generally set in a fail-safe mode, such that any interruption or malfunction of the system will result in the safety valve closing to render the well safe. '' ''' '' are fitted in almost all wells and are typically subject to rigorous local or regional legislative requirements.

packer

A downhole device used in almost every completion to isolate the annulusfrom the production conduit, enabling controlled production, injection or treatment.

bottomhole choke

A downhole device used to control fluid flow under downhole conditions. ''' are generally removable with slickline intervention and are located in a landing nipple in the tubing string.

subsurface surface controlled safety valve (SSCSV)

A downhole safety valve designed to close automatically in an emergency situation. There are two basic operating mechanisms: valves operated by an increase in fluid flow and valves operated by a decrease in ambient pressure.

surface controlled subsurface safety valve (SCSSV)

A downhole safety valve that is operated from surface facilities through a control line strapped to the external surface of the production tubing.

tubing end locator (TEL)

A downhole tool frequently used in slickline or coiled tubing tool assemblies to confirm or correlate the tool position on depth-sensitive applications. With the end of the production tubing as a known reference point, any error in measurement that may occur in reaching the treatment depth will be significantly less than what may have resulted if measuring from surface.

instrument hanger

A downhole tool on which downhole gauges or instruments that are to be temporarily left in the wellbore are attached. This device is run into the wellbore on slickline and set in a completion nipple at the required depth.

collar locator

A downhole tool or logging device used to detect and track (log) casing or tubing collars across a zone of interest, typically for correlation purposes. Most '' detect the magnetic anomaly created by the mass of the steel collar and transmit a signal to surface-display and depth correlation equipment.

reverse circulating valve

A downhole tool that is designed to enable communication between the tubing internal diameter and theannulus, typically for reverse circulation purposes, although conventional circulation often can also be undertaken. The valve design may be simple, enabling circulation without the ability to reset the tool until it is retrieved to surface, or be of a more complex design allowing several cycles between open and closed positions.

Choke Line

A high-pressure pipe leading from an outlet on the BOP stack to the backpressure choke and associated manifold.

casing collar locator (CCL)

A downhole tool used to confirm or correlate treatment depth using known reference points on thecasing string. The ''' is an electric logging tool that detects the magnetic anomalycaused by the relatively high mass of the casing collar. A signal is transmitted to surface equipment that provides a screen display and printed log enabling the output to be correlated with previous logs and known casing features such as pup joints installed for correlation purposes.

external pulling tool

A downhole tool used to pull or retrieve temporary plugs or similar equipment. The '' ''' '''engages on the external surfaces of the item to be retrieved.

internal pulling tool

A downhole tool used to pull or retrieve temporary plugs or similar equipment. This tool engages on the internal surfaces of the item to be retrieved.

tubing broach

A downhole tool used to repair damaged or collapsed tubing.incorporates a cutter profile that is forced inside the tubing by jarring or hydraulic force to re-form the tubing wall by removing tubing wall material and forcing the tubing wall into place.

Paraffin scraper or paraffin scratcher

A downhole tool, generally run on slickline, used to remove paraffin and soft wax deposits from the internal wall of production tubulars and completion equipment.

shifting tool

A downhole tool, most commonly associated with slickline operations, that is used to open, close or shift the position of downhole flow control or circulation devices, such as sliding sleeves. '' ''' generally features some means of engaging the components to be shifted and is typically run with upward or downward operating jars to deliver the necessary force or impact.

standing valve

A downhole valve assembly that is designed to hold pressure from above while allowing fluids to flow from below. generally are run and retrieved on slickline with the valve assembly located in an appropriate nipple. Applicationsinclude testing the tubing string, setting packers, or other applications in which it is desirable to maintain fluid in the tubing string.

storm choke

A downhole valve that operates by fluid velocity and closes when the fluid flow from the well exceeds preset limits.

Antiwhirl Bit

A drill bit, usually polycrystalline diamond compact bit (PDC) type, designed such that the individual cutting elements on the bit create a net imbalance force. This imbalance force pushes the bit against the side of the borehole, which in turn creates a stable rotating condition that resists backwards whirling, wobbling and downhole vibration. These type of bits allow faster rates of penetration, yet achieve longer bit life than more conventional bits, which are not dynamically biased to run smoothly, are inherently unstable, are vibration-prone and thus have shorter lives. No bit is whirl-proof, however.

settling pit OR settling tank

A drilling mud filled open steel or earthen berm tank that is not stirred or circulated. By having mud slowly pass through such a container, most large drilling solids sink to the bottom, cleaning the mud somewhat

drag bit OR polycrystalline diamond compact (PDC) bit OR fixed drag bit

A drilling tool that uses polycrystalline diamond compact (PDC) cutters to shear rock with a continuous scraping motion. These cutters are synthetic diamond disks about 1/8-in. thick and about 1/2 to 1 in. in diameter.

openhole test

A drillstem test performed in an openhole section of the wellbore. The test once was a popular method of assessing the productivity of exploration wells without the need to run casing or liner across the reservoirinterval.

cellar

A dug-out area, possibly lined with wood, cement or very large diameter (6 ft [1.8 m]) thin-wall pipe, located below the rig.

Cellar

A dug-out area, possibly lined with wood, cement or very large diameter thin-wall pipe, located below the rig. This serves as a cavity in which the casing spool and casinghead reside

Multiple-contact miscibility

A dynamic fluid-mixing process in which an injected gas exchanges components with in situ oil until the phases achieve a state of miscibility within the mixing zone of the flood front.

decollement

A fault surface parallel to a mechanically weak horizon or layer, or parallel to bedding, that detaches or separates deformed rocks above from undeformed or differently deformed rocks below. Decollements, or decollement surfaces, are typical of regions of thrust faulting such as the Alps.

box

A female threadform (internally threaded) for tubular goods and drillstring components.

sequence stratigraphy

A field of study in which basin-filling sedimentary deposits, called sequences, are interpreted in a framework of eustasy, sedimentation and subsidence through time in order to correlate strata and predict the stratigraphy of relatively unknown areas. Sequences tend to show cyclicity of changes in relative sea level and widespread unconformities, processes of sedimentation and sources of sediments, climate and tectonic activity over time. Sequence stratigraphic study promotes thorough understanding of the evolution of basins, but also allows for interpretations of potential source rocks and reservoir rocks in both frontier areas (having seismic data but little well data) and in more mature hydrocarbon provinces. Prediction of reservoir continuity is currently a key question in mature hydrocarbon provinces where sequence stratigraphy is being applied.

lamination

A fine layer (~ 1 mm thick) in strata, also called a lamina, common in fine-grained sedimentary rocks such as shale, siltstone and fine sandstone. A sedimentary bed comprises multiple laminations, or laminae.

shale

A fine-grained, fissile, detrital sedimentary rock formed by consolidation of clay- and silt-sized particles into thin, relatively impermeable layers. It is the most abundant sedimentary rock. Shale can include relatively large amounts of organic material compared with other rock types and thus has potential to become a rich hydrocarbon source rock, even though a typical shale contains just 1% organic matter. Its typical fine grain size and lack of permeability, a consequence of the alignment of its platy or flaky grains, allow shale to form a good cap rock for hydrocarbon traps. Gas shows from shales during drilling have led some shales to be targeted as potential gas reservoirs. Various clay types and volumes influence the quality of the reservoir from a petrophysical and geomechanical perspective. The quality of shale reservoirs depends on their thickness and extent, organic content, thermal maturity, depth and pressure, fluid saturations, and permeability, among other factors.

bean choke

A fixed choke used to control the flow of fluids, usually mounted on or close to the Christmas tree. A '''' contains a replaceable insert, or bean, made from hardened steel or similar durable material. The insert is manufactured with a precise diameter hole that forms the choke through which all fluids must pass. Choke inserts are available in a complete range of sizes, generally identified by choke diameter stated in 64ths of an inch; for example, a "32 bean" is equivalent to a 1/2-in. choke diameter.

plane table

A flat drawing board mounted on a tripod used in combination with an alidade to construct topographic or geologic maps in the field. A sheet of paper or mylar covering the plane table is annotated during map construction.

roughnecks

A floor hand, or member of the drilling crew who works under the direction of the driller to make or break connections as drillpipe is tripped in or out of the hole. On most drilling rigs, they are also responsible for maintaining and repairing much of the equipment found on the drill floor and derrick.

kick

A flow of formation fluids into the wellbore during drilling operations. It is physically caused by the pressure in the wellbore being less than that of the formation fluids, thus causing flow.

Annular Gas Flow

A flow of formation gas in the annulus between a casing string and the borehole wall. This occurs when there is insufficient hydrostatic pressure to restrain the gas. They can occur in uncemented intervals and even in cemented sections if the cement bond is poor. After cementing, as the cement begins to harden, a gel-like structure forms that effectively supports the solid material in the cement slurry. However, during this initial gelling period, the cement has no appreciable strength. Hence, with the solid (weighting) material now supported by the gel structure, the effective density of the slurry that the reservoir experiences falls rather suddenly to the density of the mix water of the cement, which is usually fresh water, whose density is 8.34 lbm/gal, or a gradient of 0.434 psi/ft of vertical column height. Various chemical additives have been developed to reduce annular gas flow.

Preflush

A fluid stage, normally hydrochloric acid [HCl], pumped ahead of the main treating fluid (mixture of hydrofluoric [HF] and hydrochloric [HCl] or organic acids) in a sandstone matrix-stimulation treatment.

chemical wash

A fluid, generally water-based, to thin and disperse mud in preparation for cementing. The ''' is pumped ahead of the cement slurry to help ensure effective mud removal and efficient cement placement. Other specialized ''' may be used in the remedial treatment of scales orparaffin deposits in production tubulars.

turbulent flow

A fluid-flow regime characterized by swirling or chaotic motion as the fluid moves along the pipe or conduit. The linear velocity of the fluid particles is similar regardless of position in the conduit, although particles close to the conduit walls have a lower velocity. This characteristic makes '' flow an efficient flow regime for the pickup and transport of solids. However, the potential for erosion may be significant, especially with abrasive fluids and a tortuous flow path.

thief zone

A formation encountered during drilling into which circulating fluids can be lost.

charged zone

A formation interval that has become overpressured by the injection of drilling or treatment fluids.

Gravity-stable displacement

A frontal advance in which gravity and viscous forces are in equilibrium, resulting in a stable, highly efficient frontal advance.

choke line

A high-pressure pipe leading from an outlet on the BOP stack to the backpressure choke and associated manifold. During well-control operations, the fluid under pressure in the wellbore flows out of the well through this pipe to the choke, reducing the fluid pressure to atmospheric pressure.

float Joint / shoe joint

A full-sized length of casing placed at the bottom of the casing string that is usually left full of cement on the inside to ensure that good cement remains on the outside of the bottom of the casing. If cement were not left inside the casing in this manner, the risk of overdisplacing the cement (due to improper casing volume calculations, displacement mud volume measurements, or both) would be significantly higher.

float joint

A full-sized length of casing placed at the bottom of the casing string that is usually left full of cement on the inside to ensure that good cement remains on the outside of the bottom of the casing. If cement were not left inside the casing in this manner, the risk of overdisplacing the cement (due to improper casing volume calculations, displacement mud volume measurements, or both) would be significantly higher.

gas-lift mandrel

A gas-lift system component that is assembled with the production tubing string to provide a means of locating gas-lift valves. The position or depth of the gas lift valves is crucial to the efficient operation of the entire system. Consequently, proper assembly of the '' '' '' within the completion tubularsis essential. A port in the '' '' '' provides communication between the lift-gas supply in the tubing annulus and the production-tubing conduit.

Vaporizing drive

A gasflood process in which a lean gas, for example methane, nitrogen or carbon dioxide, is injected into a reservoir to achieve multiple-contact miscibility. Upon contact with the oil, light and intermediate molecular-weight hydrocarbons transfer from the oil into the gas phase.

Thermal recovery

A general term for injection processes that introduce heat into a reservoir. Used to produce oils with an API gravity < 20.

Miscible displacement

A general term for injection processes that introduce miscible gases into the reservoir.

formation damage

A general term to describe the reduction in permeability to the near-wellbore area of a reservoirformation. There are several recognized damage mechanisms, such as the invasion of incompatible fluids swelling the formation clays, or fine solids from dirty fluids plugging the formation matrix. Because '' '' can significantly affect the productivity of any well, adequate precautions should be exercised to avoid damage during all phases in the life of a well.

casing test

A general term used to describe a drillstem test (DST) performed in cased hole.

running tool

A generic name for a tool or device that is used in the placement or setting of downhole equipment such as permanent packers or plugs. can be retrieved after the operation or setting process. In some cases, also is used to retrieve the equipment or tool that has been set in the wellbore.

polished joint

A generic term for a completion component that has been polished or prepared to enable an efficient hydraulic seal.

mobile offshore drilling unit (MODU)

A generic term for several classes of self-contained floatable or floating drilling machines such as jackups, semisubmersibles, and submersibles.

gumbo

A generic term for soft, sticky, swelling clay formations that are frequently encountered in surface holes offshore or insedimentary basins onshore near seas. This clay fouls drilling tools and plugs piping, both severe problems for drilling crews.

tubulars

A generic term pertaining to any type of oilfield pipe, such as drill pipe, drill collars, pup joints, casing, production tubing andpipeline.

produced fluid

A generic term used in a number of contexts but most commonly to describe any fluid produced from a wellbore that is not a treatment fluid.

rupture disk

A high-precision component designed to rupture with the application of a predetermined hydraulicpressure. '' '' are commonly used in downhole applications in which the controlled application of pump pressure is used to set or operate downhole equipment, such as packers or plugs. In some applications, a '' '' may be used as a protection device to prevent overpressurizing a vessel or component.

cement

A generic term used to describe Portland cement used in oil- and gas-well applications. In its simplest form, cement powder is ground from kiln-fired limestone and clay. However, modern oilfield cements are precise blends of quality assured materials to achieve consistent and predictable performance. Cement sets as the water in the slurry reacts chemically with the active ingredients, the most significant of which is tricalcium silicate reacting to create calcium silicate hydrate. Cement additives are used to control the setting process of the cement slurry and enhance the performance of the set cement. The API has developed a classification system for oilwell cement specification and performance.

casing hardware

A generic term used to describe equipment attached to, and run with, thecasing string. Commonly used ''' includes guide or float shoes, float or landing collars, centralizers, scratchers and cement baskets. More specialized ''' may include stage-cementing collars, differential fill-up equipment and other specialized equipment to help achieve successful placement and cementation of the casing string.

sand

A generic term used to describe small formation particles known as fines that may be produced with thereservoir fluid.

completion

A generic term used to describe the assembly of downhole tubulars and equipment required to enable safe and efficient production from an oil or gas well. The point at which the completion process begins may depend on the type and design of well. However, there are many options applied or actions performed during the construction phase of a well that have significant impact on the productivity of the well.

disconformity

A geologic surface that separates younger strata from older strata and represents a time of nondeposition, possibly combined with erosion. Some disconformities are highly irregular whereas others have no relief and can be difficult to distinguish within a series of parallel strata.

structure

A geological feature produced by deformation of the Earth's crust, such as a fold or a fault; a feature within a rock, such as a fracture or bedding surface; or, more generally, the spatial arrangement of rocks.

unconformity

A geological surface separating older from younger rocks and representing a gap in the geologic record. Such a surface might result from a hiatus in deposition of sediments, possibly in combination with erosion, or deformation such as faulting. An angular unconformity separates younger strata from eroded, dipping older strata. A disconformity represents a time of nondeposition, possibly combined with erosion, and can be difficult to distinguish within a series of parallel strata. A nonconformity separates overlying strata from eroded, older igneous or metamorphic rocks. The study and interpretation of unconformities locally, regionally and globally is the basis of sequence stratigraphy.

chronostratigraphic chart

A graphic display, with geologic time along the vertical axis and distance along the horizontal axis, to demonstrate the relative ages and geographic extent of strata or stratigraphic units in a given area, also known as a Wheeler diagram. In addition, information from seismic data, well logs and rock samples, and biostratigraphic and lithostratigraphic information can be shown within each chronostratigraphic unit. A chronostratigraphic chart can concisely illustrate sequence stratigraphic interpretations.

fence diagram

A graphical display of three-dimensional data and interpretations in two-dimensional perspective view. Geologic cross sections can be displayed in a network to form a fence diagram. Stratigraphic changes can be displayed clearly in fence diagrams.

Pressure-composition diagram

A graphical representation indicating phase behavior for variation of saturation pressure and injection gas concentration at a given temperature. The diagram indicates conditions for single-phase and two-phase behavior and, within the two-phase region, lines of constant volume fraction, termed quality lines. The diagram is constructed using swelling test saturation pressures and liquid volumes.

Ternary diagram

A graphical representation of concentrations in a system with three components.

glauconite

A green silicate mineral found in sedimentary rocks and formed on continental shelves characterized by slow sedimentation and organic matter, such as fecal pellets, present in an oxidizing environment. In sufficient quantity, it can form a sandy, green deposit such as the Cretaceous greensands of the US and UK.

illite

A group of clay minerals formed during the alteration of silicate minerals such as mica and feldspar and commonly found in marine shales.

smectite

A group of clay minerals that includes montmorillonite. This type of mineral tends to swell when exposed to water. Bentonite includes minerals of the smectite group.

carbonate (adjective)

A group of minerals found mostly in limestone and dolostone that includes aragonite, calcite and dolomite. Calcite is the most abundant and important of the carbonate minerals.

sequence

A group of relatively conformable strata that represents a cycle of deposition and is bounded by unconformities or correlative conformities. Sequences are the fundamental unit of interpretation in sequence stratigraphy. Sequences comprise systems tracts.

silicate mineral

A group of rock-forming minerals in which SiO4 tetrahedra combine with cations. These minerals are the most abundant type of mineral. Olivine, pyroxene, amphibole, mica, quartz and feldspar are types of silicate minerals.

feldspar

A group of rock-forming silicate minerals that are essential constituents of igneous rocks and are common in sandstones. Feldspar can weather to form clay minerals. Feldspar can occur in all three major rock types and forms approximately 60% of the crust of the Earth.

mica

A group of sheet silicates characterized by a platy appearance and basal cleavage most common in igneous and metamorphic rocks. Several clay minerals, such as chlorite and glauconite, are closely related to the mica group.

kill line

A high-pressure pipe leading from an outlet on the BOP stack to the high-pressure rig pumps. During normal well control operations, kill fluid is pumped through the drillstring and annular fluid is taken out of the well through the choke line to the choke, which drops the fluid pressure to atmospheric pressure.

nitrogen unit

A high-pressure pump or compressor unit capable of delivering high-purity nitrogen gas for use in oil or gas wells.

elevator

A hinged mechanism that may be closed around drillpipe or other drillstringcomponents to facilitate lowering them into the wellbore or lifting them out of the wellbore. In the closed position, its arms are latched together to form a load-bearing ring around the component. In the open position, the device splits roughly into two halves and may be swung away from the drillstring component.

bit record

A historical record of how a bit performed in a particular wellbore. The bit record includes such data as the depth the bit was put into the well, the distance the bit drilled, the hours the bit was being used "on bottom" or "rotating", the mud type and weight, the nozzle sizes, the weight placed on the bit, the rotating speed and hydraulic flow information

drainhole

A hole or short conduit through which fluids can flow. In equipment applications, a ''' is generally made to avoid the buildup of pressure within a nonpressure area, such as may occur in the event of a leak in a pressure housing within a tool assembly.

drain hole

A hole or short conduit through which fluids can flow. In equipment applications, a ''''' is generally made to avoid the buildup of pressure within a nonpressure area, such as may occur in the event of a leak in a pressure housing within a tool assembly.

hardground

A horizon cemented by precipitation of calcite just below the sea floor. Local concretions form first in a hardground and can be surrounded by burrows of organisms until the cement is well developed.

paraffin

A hydrocarbon compound that often precipitates on production components as a result of the changing temperatures and pressures within the production system. occur as wax-like substances that may build up on the completion components and may, if severe, restrict production.

desander

A hydrocyclone device that removes large drill solids from the whole mudsystem. It should be located downstream of the shale shakers and degassers, but before the desilters or mud cleaners.

desilter

A hydrocyclone much like a desander except that its design incorporates a greater number of smaller cones. As with the desander, its purpose is to remove unwanted solids from the mud system.

flag joint

A joint of tubing or casing included in the string at a known position to provide a reference point for further operations. A short pup joint that registers clearly in a collar locator log is a common ''' '''.

contingency plan

A key component of the operational planning process that takes account of reasonably foreseeable events that may prevent completion of normal operations. The formal plans and procedures for any operation should include normal operating procedures, ''' and emergency responses.

Rising bubble aparatus

A laboratory device used to indicate miscibility between reservoir oil and injection gas. A gas bubble is injected into an oil-filled visual cell at a given temperature and test pressure. The change in shape of the rising bubble indicates its miscibility with the oil at those conditions. Below the minimum miscibility pressure (MMP), the bubble holds its shape as it rises. Above the MMP, the bubble shape changes as it rises; it may disintegrate, dissolve or disappear into the oil. Testing at several pressures helps determine the MMP between the gas and oil.

Slim-tube test

A laboratory test used to estimate the minimum miscibility pressure (MMP) or minimum miscibility concentration (MMC) of a given injection solvent and reservoir oil.

contour

A line on a map that represents a constant value of the parameter being mapped. This line includes points of equal value and separates points of higher value from points of lower value. Contours are commonly drawn on maps to portray the structural configuration of the Earth's surface or formations in the subsurface. For example, structure maps contain contours of constant elevation with respect to a datum (such as sea level). Contours are also used to interpret subsurface configurations of rock bodies in areas of limited control, such as drawing contours of the thickness of a common rock unit in several widely separated wells to extrapolate its thickness in a nearby undrilled location.

channel

A linear, commonly concave-based depression through which water and sediment flow and into which sediment can be deposited in distinctive, often elongated bodies. Channels can occur in a variety of morphologies, e.g., straight, meandering or braided. In some areas, coarse sediments can fill channels of streams or rivers that cut through finer grained sediments or rocks. The close proximity of coarse-grained and fine-grained sediments can ultimately lead to the formation of stratigraphic hydrocarbon traps.

tally

A list containing details of tubulars that have been prepared for running, or that have been retrieved from the wellbore. Each tubing joint is numbered and the corresponding length and other pertinent details noted alongside.

casing collar log

A log provided by a casing collar locator tool that generally incorporates a gamma ray log to correlatethe relative position of casing string features, such as the location of a pup joint, with the reservoir or formation of interest.

collar log

A log showing the depth or relative position of casing or tubing collars that is used to correlate depth for depth-sensitive applications such as perforating or isolation treatments. Indications are provided by acollar locator tool and correlations are made with previous baseline logs, such as the gamma ray log, or the casing or tubing running tally prepared during the installation process.

lineament

A long linear or gently curving feature on the surface of a terrestrial planet or moon that is suggestive of an underlying geologic structure or contact. Most lineaments are identified through remote sensing, such as satellite imagery or topographic, gravimetric and magnetic data.

Coiled Tubing or CT

A long, continuous length of pipe wound on a spool. The pipe is straightened prior to pushing into a wellbore and rewound to coil the pipe back onto the transport and storage spool.

coiled tubing (CT) OR endless tubing OR reeled tubing

A long, continuous length of pipe wound on a spool. The pipe is straightened prior to pushing into a wellbore and rewound to coil the pipe back onto the transport and storage spool.

lubricator

A long, high-pressure pipe fitted to the top of a wellhead or Christmas tree so that tools may be put into a high-pressure well. The top of the pipe assembly includes a high-pressure grease-injection section and sealing elements. The pipe is installed on top of the tree and tested, the tools placed in the lubricator and the lubricator pressurized to wellbore pressure.

Cat Walk

A long, rectangular platform about 3 ft [0.9 m] high, usually made of steel and located perpendicular to the vee-door at the bottom of the slide. This platform is used as a staging area for rig and drillstring tools, components that are about to be picked up and run, or components that have been run and are being laid down.

catwalk

A long, rectangular platform about 3 ft [0.9 m] high, usually made of steel and located perpendicular to the vee-door at the bottom of the slide. This platform is used as a staging area for rig and drillstringtools, components that are about to be picked up and run, or components that have been run and are being laid down.

condensate

A low-density, high-API gravity liquid hydrocarbon phase that generally occurs in association with natural gas. Its presence as a liquid phase depends on temperature and pressure conditions in the reservoir allowing condensation of liquid from vapor. The production of condensate reservoirs can be complicated because of the pressure sensitivity of some condensates: During production, there is a risk of the condensate changing from gas to liquid if the reservoir pressure drops below the dew point during production. Reservoir pressure can be maintained by fluid injection if gas production is preferable to liquid production. Gas produced in association with condensate is called wet gas. The API gravity of condensate is typically 50 degrees to 120 degrees.

base map

A map on which primary data and interpretations can be plotted. It typically includes locations of lease or concession boundaries, wells, seismic survey points and other cultural data such as buildings and roads, with a geographic reference such as latitude and longitude or Universal Transverse Mercator (UTM) grid information. Geologists use topographic maps as base maps for construction of surface geologic maps. Geophysicists typically use shot point maps, which show the orientations of seismic lines and the specific points at which seismic data were acquired, to display interpretations of seismic data. In the field, geologists can use a plane table and alidade to construct a base map.

geologic map

A map showing the type and spatial distribution of rocks at the surface of the Earth. Rock formations are color-coded and symbols for geological structures are annotated, so age relationships are evident. Topographic contours and cultural features can also appear on geologic maps.

lithofacies

A mappable subdivision of a stratigraphic unit that can be distinguished by its facies or lithology-the texture, mineralogy, grain size, and the depositional environment that produced it.

drill ship

A maritime vessel modified to include a drilling rig and special station-keeping equipment. The vessel is typically capable of operating in deep water.

bentonite

A material composed of clay minerals, predominantly montmorillonite with minor amounts of other smectite group minerals, commonly used in drilling mud. Bentonite swells considerably when exposed to water, making it ideal for protecting formations from invasion by drilling fluids. Montmorillonite forms when basic rocks such as volcanic ash in marine basins are altered.

productivity index (PI)

A mathematical means of expressing the ability of a reservoir to deliver fluids to the wellbore. The'' ''' is usually stated as the volume delivered per psi of drawdown at the sandface (bbl/d/psi).

tubing performance curve (TPC)

A mathematical tool used in production engineering to assess the performance of the completion string by plotting the surface production rate against the flowing bottomhole pressure. The fluid composition and behavior of the fluid phases in the specific completion design will determine the shape of the curve.

inflow performance relationship

A mathematical tool used in production engineering to assess well performance by plotting the well production rate against the flowingbottomhole pressure (BHP). The data required to create the IPR are obtained by measuring the production rates under various drawdown pressures. Thereservoir fluid composition and behavior of the fluid phases under flowing conditions determine the shape of the curve.

pressure transient test

A means of assessing reservoir performance by measuring flow rates and pressures under a range of flowing conditions and applying the data to a mathematical model. Fundamental data relating to the interval under test, such as reservoir height and details of the reservoir fluids, are also input.

sand consolidation

A means of controlling the undesirable production of sand from weak sandstone formations. '' ''' chemically binds the grains of sand that make up the formation matrix while maintaining sufficient permeability to achieve viable production rates.

Viscous forces

A measure of a fluid's resistance to flow. These forces in a fluid are proportional to the rate at which the fluid velocity is changing in space.

unconfined compressive strength

A measure of a material's strength. The unconfined compressive strength (UCS) is the maximum axial compressive stress that a right-cylindrical sample of material can withstand under unconfined conditions—the confining stress is zero. It is also known as the uniaxial compressive strength of a material because the application of compressive stress is only along one axis—the longitudinal axis—of the sample.

uniaxial compressive strength

A measure of a material's strength. The uniaxial compressive strength (UCS) is the maximum axial compressive stress that a right-cylindrical sample of material can withstand before failing. It is also known as the unconfined compressive strength of a material because confining stress is set to zero.

tortuosity

A measure of deviation from a straight line. It is the ratio of the actual distance traveled between two points, including any curves encountered, divided by the straight line distance. Tortuosity is used by drillers to describe wellbore trajectory, by log analysts to describe electrical current flow through rock and by geologists to describe pore systems in rock and the meander of rivers.

Sweep efficiency

A measure of the effectiveness of an enhanced oil recovery process that depends on the volume of the reservoir contacted by the injected fluid.

hydraulic horsepower OR HHP

A measure of the energy per unit of time that is being expended across the bit nozzles. It is commonly calculated with the equation P*Q/1714, where P stands for pressure in pounds per square in., Q stands for flow rate in gallons per minute, and 1714 is a conversion factor necessary to yield the result in terms of horsepower.

tortuosity

A measure of the geometric complexity of a porous medium. This is a ratio that characterizes the convoluted pathways of fluid diffusion and electrical conduction through porous media. In the fluid mechanics of porous media, tortuosity is the ratio of the length of a streamline—a flow line or path—between two points to the straight-line distance between those points. Tortuosity is thus related to the ratio of a fluid's diffusion coefficient when it is not confined by a porous medium to its effective diffusion coefficient when confined in a porous medium. Tortuosity is also related to the formation factor, which is the ratio of electrical resistivity of a conductive fluid in a porous medium to the electrical resistivity of the fluid itself.

relative permeability

A measurement of the ability of two or more fluid phases to pass through a formation matrix.

vitrinite reflectance

A measurement of the maturity of organic matter with respect to whether it has generated hydrocarbons or could be an effective source rock.

reservoir height

A measurement of the vertical thickness of reservoir formation that is open to flow.used in calculations and mathematical models to assess reservoir performance or potential productivity.

kelly spinner

A mechanical device for rotating the kelly, typically pneumatic. It is a relatively low torque device, useful only for the initial makeup of threaded tool joints. It is not strong enough for proper torque of the tool joint or for rotating thedrillstring itself.

Casing Centralizer

A mechanical device that keeps casing from contacting the wellbore wall. A continuous 360-degree annular space around casing allows cement to completely seal the casing to the borehole wall.

casing centralizer

A mechanical device that keeps casing from contacting the wellbore wall. A continuous 360-degreeannular space around casing allows cement to completely seal the casing to the borehole wall.

check valve

A mechanical device that permits fluid to flow or pressure to act in one direction only. ''' are used in a variety of oil and gas industry applications as control or safety devices. ''' designs are tailored to specific fluid types and operating conditions. Some designs are less tolerant of debris, while others may obstruct the bore of the conduit or tubing in which the check valve is fitted.

swivel

A mechanical device that suspends the weight of the drillstring. It is designed to allow rotation of the drillstring beneath it conveying high volumes of high-pressure drilling mud between the rig's circulation system and the drillstring.

jar

A mechanical device used downhole to deliver an impact load to another downhole component, especially when that component is stuck. There are two primary types, hydraulic and mechanical

jar

A mechanical device used downhole to deliver an impact load to another downhole component, especially when that component is stuck. There are two primary types, hydraulic and mechanical. Energy is stored in the drillstring and suddenly released by this mechanical device when it fires. The principle is similar to that of a carpenter using a hammer. Kinetic energy is stored in the hammer as it is swung, and suddenly released to the nail and board when the hammer strikes the nail. This device can be designed to strike up, down, or both.

anhydrite

A member of the evaporite group of minerals and the soft rock comprising this formed by precipitation of calcium sulfate from evaporation of seawater. Anhydrite can also form through the dehydration of gypsum, another sulfate mineral found in evaporites. Anhydrite may occur as a cap rock above salt domes.

gravel pack screen

A metal filter assembly used to support and retain the sand placed during gravel pack operations. A range of sizes and screen configurations is available to suit the characteristics of the wellbore, production fluid and the formationsand.

Bow-Spring Centralizer

A metal strip shaped like a hunting bow and attached to a tool or to the outside of casing. These are used to keep casing in the center of a wellbore or casing prior to and during a cement job.

Improved oil recovery

A method for recovering additional oil beyond fluid expansion, rock compressibility, gravitational drainage, pressure decline and natural waterdrive or gasdrive. This term is used in both a restricted sense and a more general sense. In its restricted sense, it is a process, such as waterflooding or gasflooding, that adds energy to a reservoir to stimulate oil production and increase recovery factor. In its more general sense, it is any activity that increases oil production and increases the recovery factor. This sense can also include, for example, enhanced oil recovery methods, infill drilling, hydraulic fracturing, and drilling horizontal and multilateral wells.

Cable Tool Drilling or Basket Sub Drilling

A method of drilling whereby an impact tool or bit, suspended in the well from a steel cable, is dropped repeatedly on the bottom of the hole to crush the rock. After a few impacts on the bottom of the hole, the cable is reeled in and the cuttings basket emptied, or a bailer is used to remove cuttings from the well

cable-tool drilling

A method of drilling whereby an impact tool or bit, suspended in the well from a steel cable, is dropped repeatedly on the bottom of the hole to crush the rock. The tool is usually fitted with some sort of cuttingsbasket to trap the cuttings along the side of the tool.

cable-tool drilling

A method of drilling whereby an impact tool or bit, suspended in the well from a steel cable, is dropped repeatedly on the bottom of the hole to crush the rock. The tool is usually fitted with some sort of cuttingsbasket to trap the cuttings along the side of the tool. After a few impacts on the bottom of the hole, the cable is reeled in and the cuttings basket emptied, or a bailer is used to remove cuttings from the well. The tool is reeled back to the bottom of the hole and the process repeated. Limited to shallow depths, almost obsolete.

rotary drilling

A method of making hole that relies on continuous circular motion of the bit to break rock at the bottom of the hole. This method, made popular after the discovery of the East Texas Field by "Dad" Joiner in 1930, is much more efficient than the alternative, cable tool drilling.

Water flood

A method of secondary recovery in which water is injected into the reservoir formation to displace residual oil.

waterflood

A method of secondary recovery in which water is injected into the reservoir formation to displace residual oil. The water from injection wells physically sweeps the displaced oil to adjacent productionwells.

In-situ combustion

A method of thermal recovery in which fire is generated inside the reservoir by injecting a gas containing oxygen, such as air. A special heater in the well ignites the oil in the reservoir and starts a fire.

Hot waterflooding

A method of thermal recovery in which hot water is injected into a reservoir through specially distributed injection wells. It reduces the viscosity of the crude oil, allowing it to move more easily toward production wells.

Steam flood

A method of thermal recovery in which steam generated at surface is injected into the reservoir through specially distributed injection wells.

steamflood

A method of thermal recovery in which steam generated at surface is injected into the reservoir through specially distributed injection wells. When steam enters the reservoir, it heats up the crude oil and reduces its viscosity. The heat also distills light components of the crude oil, which condense in the oil bank ahead of the steam front, further reducing the oil viscosity. The hot water that condenses from the steam and the steam itself generate an artificial drive that sweeps oil toward producing wells.

mud pulse telemetry

A method of transmitting LWD and MWD data acquired downhole to the surface, using pressure pulses in the mud system. The measurements are usually converted into an amplitude- or frequency-modulated pattern of mud pulses. The same system is used to transmit commands from the surface.

diatom

A microscopic, single-celled, freshwater or saltwater algae that has a silica-rich cell wall called a frustule. Diatoms are so abundant that they can form thick layers of sediment composed of the frustules of the organisms that died and sank to the bottom. Frustules have been an important component of deep-sea deposits since Cretaceous time. Diatomite is the sedimentary rock that forms from diatom frustules.

Scale

A mineral deposit that can occur in the tubing, the gravel pack, the perforations or the formation. Deposition of this substance occurs when the solution equilibrium of the water is disturbed by pressure and temperature changes, dissolved gases or incompatibility between mixing waters.

scale

A mineral salt deposit that may occur on wellbore tubulars and components as the saturation of produced water is affected by changing temperature andpressure conditions in the production conduit.

antithetic fault

A minor, secondary fault, usually one of a set, whose sense of displacement is opposite to its associated major and synthetic faults. Antithetic-synthetic fault sets are typical in areas of normal faulting.

Mud acid

A mixture of hydrofluoric acid [HF] and hydrochloric acid [HCl] or organic acid used as the main fluid in a sandstone matrix treatment.

mud acid

A mixture of hydrofluoric acid [HF] and hydrochloric acid [HCl] or organic acid used as the main fluid in asandstone matrix treatment. Hydrochloric acid or organic acid is mixed with HF to keep the pH low when it spends, thereby preventing detrimental precipitates.

hydrofluoric hydrochloric acid

A mixture of hydrofluoric acid [HF] and hydrochloric acid [HCl] or organic acid used as the main fluid in asandstone matrix treatment. Hydrochloric acid or organic acid is mixed with HF to keep the pH low when it spends, thereby preventing detrimental precipitates. The name mud acid was given to these mixtures because they were originally developed to treat damage from siliceous drilling muds.

Non-wetting phase

A phase that does not preferentially wet the solid surface

Hydrofluoric-hydrochloric acid

A mixture of two acids used as the main fluid in a sandstone matrix treatment. The mixture keep the pH low when it spends, thereby preventing detrimental precipitates. The name mud acid was given to these mixtures because they were originally developed to treat damage from siliceous drilling muds.

reef

A mound, ridge, or buildup of sediment or sedimentary rock, most commonly produced by organisms that secrete shells such as corals. These are typically taller than the sediment that surrounds them, resistant to weathering and wave action, and preserved within sediment of a different composition. Carbonate reefs form in a limited range of temperatures, water depths, salinities and wave activities, so their occurrence can be used to interpret past environmental conditions. Because the rocks that surround reefs can differ in composition and permeability, porous reefs can form stratigraphic traps for hydrocarbons. Porosity of reefal limestones depends on post-depositional diagenetic changes.

steerable motor

A mud motor incorporating a bent housing that may be stabilized like a rotary bottomhole assembly.

suction pit

A mud tank, usually made of steel, connected to the intake of the main rig pumping system. The connection is commonly formed with a centrifugal pump charging the main rig pumps to increase efficiency. Since it is the last tank in the surface mud system, the suction pit should contain the cleanest and best-conditioned mud on location. It is also the most representative of mud characteristics in the hole, except for temperature.

transition flow

A multiphase flow regime in near-vertical pipes in which large, irregular slugs of gas move up the center of the pipe, usually carrying droplets of oil or water with them. Most of the remaining oil or water flows up along the pipe walls. The flow is relatively chaotic, producing a frothy mixture. Unlike slug flow, neither phase is continuous. The gas slugs are relatively unstable, and take on large, elongated shapes. Also known as churn flow, this flow is an intermediate flow condition between slug flow and mist flow, and occurs at relatively high gasvelocity. As the gas velocity increases, it changes into annular flow.

churn flow

A multiphase flow regime in near-vertical pipes in which large, irregular slugs of gas move up the center of the pipe, usually carrying droplets of oil or water with them. Most of the remaining oil or water flows up along the pipe walls. The flow is relatively chaotic, producing a frothy mixture. Unlike slug flow, neither phase is continuous. The gas slugs are relatively unstable, and take on large, elongated shapes. Also known as transition flow, this flow is an intermediate flow condition between slug flow and mist flow, and occurs at relatively high gas velocity. As the gas velocity increases, it changes into annular flow.

froth flow

A multiphase flow regime in near-vertical pipes in which large, irregular slugs of gas move up the center of the pipe, usually carrying droplets of oil or water with them. Most of the remaining oil or water flows up along the pipe walls. The flow is relatively chaotic, producing a frothy mixture. Unlike slug flow, neither phase is continuous. The gas slugs are relatively unstable, and take on large, elongated shapes. Also known as transition flow, this flow is an intermediateflow condition between slug flow and mist flow, and occurs at relatively high gas velocity. As the gas velocity increases, it changes into annular flow.

bubble flow

A multiphase fluid flow regime characterized by the gas phase being distributed as bubbles through the liquid phase. In a producing wellbore where the bubbles are uniformly distributed, there is little relative motion between the phases. Where the bubbles congregate and combine to form a less uniform distribution of the gas phase, some slippage will occur between the phases with the gas tending to cut through the liquid phase.

bubble flow

A multiphase fluid-flow regime characterized by the gas phase being distributed as bubbles through the liquid phase. In a producing wellbore where the bubbles are uniformly distributed, there is little relative motion between the phases. Where the bubbles congregate and combine to form a less uniform distribution of the gas phase, some slippage will occur between the phases with the gas tending to cut through the liquid phase

slug flow

A multiphase-fluid flow regime characterized by a series of liquid plugs (slugs) separated by a relatively large gas pockets. In vertical flow, the bubble is an axially symmetrical bullet shape that occupies almost the entire cross-sectional area of the tubing. The resulting flow alternates between high-liquid and high-gas composition.

salt dome

A mushroom-shaped or plug-shaped diapir made of salt, commonly having an overlying cap rock. Salt domes form as a consequence of the relative buoyancy of salt when buried beneath other types of sediment. The salt flows upward to form salt domes, sheets, pillars and other structures. Hydrocarbons are commonly found around salt domes because of the abundance and variety of traps created by salt movement and the association with evaporite minerals that can provide excellent sealing capabilities.

seep

A naturally occurring, typically slow leakage of fluid—water, oil or gas—at the Earth's surface. This results from migration of the fluid from its source or reservoir formation because the formation pressure exceeds the formation's seal capacity such as during rapid loading of the overburden by sedimentation or during fluid expansion or from damage to the seal such as by faulting or tectonism.

weathered layer

A near-surface, possibly unconsolidated layer of low seismic velocity. The base of the weathered layer commonly coincides with the water table and a sharp increase in seismic velocity. The weathered layer typically has air-filled pores.

no go landing nipple

A nipple that incorporates a reduced diameter internal profile that provides a positive indication of seating by preventing the tool or device to be set from passing through the nipple. In many completions, a '' '' '' '' is preferred for the deepest nipple location, providing a no-go barrier to protect against a tool string being run or dropped below the tubing string.

Vapor extraction

A non-thermal heavy oil production method. A solvent vapor is used to reduce viscosity of the heavy oil.

listric fault

A normal fault that flattens with depth and typically found in extensional regimes. This flattening manifests itself as a curving, concave-up fault plane whose dip decreases with depth.

Hydrophile-lipophile balance number

A number on the scale of one to 40 according to the HLB system, introduced by Griffin (1949 and 1954). The HLB system is a semi-empirical method to predict what type of surfactant properties a molecular structure will provide. Water-in-oil emulsifiers have a low HLB numbers, typically around 4. Solubilizing agents have high HLB numbers. Oil-in-water emulsifiers have intermediate to high HLB numbers.

drillable packer

A packer assembly that can be removed from the wellbore only by drilling or milling. ''''', and similar tools such as bridge plugs, are typically made from cast iron, aluminum, plastic or similar brittle materials.

tool joint

A part at the end of tubulars, such as drillpipe, casing or other tubing, which has extra thickness and strength to compensate for the loss of metal in the threaded ends.

threadform

A particular style or type of threaded connection, especially as used for rotary shouldered connections.

semisubmersible

A particular type of floating vessel that is supported primarily on large pontoon-like structures submerged below the sea surface. The operating decks are elevated perhaps 100 or more feet above the pontoons on large steel columns

transform fault

A particular type of strike-slip fault that is a boundary of an oceanic tectonic plate. The actual movement of a transform fault is opposite to its apparent displacement because of the interplay of spreading and faulting between tectonic plates.

hostile environment

A particularly difficult set of well conditions that may detrimentally affect steel, elastomers, mud additives, electronics, or tools and tool components. Such conditions typically include excessive temperatures, the presence of acid gases (H2S, CO2), chlorides, high pressures and, more recently, extreme measured depths.

cleanup

A period of controlled production, generally following a stimulation treatment, during which time treatment fluids return from the reservoir formation. Depending on the treatment, the '''' period can be relatively short and uncomplicated. However, following more complex treatments such as gravel packor hydraulic fracturing, the ''' process should be conducted carefully to avoid jeopardizing the long-term efficiency of the treatment.

scout

A petroleum industry worker who tracks competitive exploration and production activity, either for a company or on a free-lance basis. Scouts can facilitate trading of technical data such as well logs among companies before such data enter the public domain unless the operations or data are held "tight."

Liquid blocking

A phenomenon encountered during dry forward combustion in which an oil zone around the production well cannot be pushed forward by the heated oil. The fluid located in this zone is still at the original reservoir temperature. Therefore, the fluid is still highly viscous and normally not mobile.

Gravity override

A phenomenon of multiphase flow in a reservoir in which a less dense fluid flows preferentially on the top of a reservoir unit and a more dense fluid flows at the bottom. For example, in a steamflood, steam flows on the top and condensed liquid flows at the bottom of the zone. This causes sweep inhomogeneities that can be mitigated through foam flooding.

differential compaction

A phenomenon that occurs after the deposition of some sediments such that different parts of the sedimentary accumulation develop different degrees of porosity or settle unevenly during burial beneath successive layers of sediment. This can result from location on an uneven surface, such as near and over a reef structure, or near a growth fault, or from different susceptibility to compaction. The porosity in a formation that has experienced differential compaction can vary considerably from one area to another.

Fluid pound

A phenomenon that occurs when the downhole pump rate exceeds the production rate of the formation. It can also be due to the accumulation of low-pressure gas between the valves. On the downstroke of the pump, the gas is compressed, but the pressure inside the barrel does not open the traveling valve until the traveling valve strikes the liquid. Finally when the traveling valve opens, the weight on the rod string can suddenly drop thousands of pounds in a fraction of a second. This condition should be avoided because it causes extreme stresses, which can result in premature equipment failure. Slowing down the pumping unit, shortening the stroke length or installing a smaller bottom hole pump can correct this problem.

subduction

A plate tectonic process in which one lithospheric plate descends beneath another into the asthenosphere during a collision at a convergent plate margin. Because of the relatively higher density of oceanic lithosphere, it will typically descend beneath the lighter continental lithosphere during a collision. In a collision of plates of continental lithosphere, the density of the two plates is so similar that neither tends to be subducted and mountains form. As a subducted plate descends into the asthenosphere, Earthquakes can occur, especially in the Wadati-Benioff zone, but, if the plate descends deeply into the mantle, it will eventually be heated to the point of melting. Volcanoes can form above a descending plate.

barite plug

A plug made from barite weighting materials that is placed at the bottom of a wellbore. Unlike a cement plug, the settled solids do not set solid, yet a '' can provide effective and low-cost pressureisolation. A '' is relatively easy to remove and is often used as a temporary facility for pressure isolation or as a platform enabling the accurate placement of treatments above the plug.

balanced plug

A plug of cement or similar material placed as a slurry in a specific location within the wellbore and which has set to provide a means of pressure isolation or mechanical platform. For correct placement, the volume of slurry and the displacement fluid must be carefully calculated and measured. The correct volume ensures that the column of fluid in the tubing string is balanced by the column of fluid in theannulus.

thread rule

A pocket-size thread gauge used in field operations to correctly identify or confirm the thread type and size of tubular goods.

depth reference point

A point within the wellbore from which accurate depth measurements can be made, such as the end of the tubing string, or a nipple or similar completion component.

HF

A poisonous liquid acid composed of hydrogen and fluorine. ....... is used primarily because it is the only common, inexpensive mineral acid that can dissolve siliceous minerals. .... is typically mixed with hydrochloric acid [HCl] or organic acid to keep the pH low when it spends, thereby preventing detrimental precipitates. These mixtures, also called mud acids, are considered the main fluid in a sandstone acid treatment because they remove formation damage.

Hydrofluoric acid

A poisonous liquid acid composed of hydrogen and fluorine. It is used primarily because it is the only common, inexpensive mineral acid that can dissolve siliceous minerals.

sealbore

A polished bore designed to accept a seal assembly, such as may be used in a permanent productionpacker.

Polyacrylamide

A polymer with a high molecular weight. Each repeating monomer is a combination of carbon, hydrogen, oxygen and nitrogen. Frequently used as a mobility control buffer in micellar-polymer-floods.

chalk

A porous marine limestone composed of fine-grained remains of microorganisms with calcite shells, coccolithophores, such as the White Cliffs of Dover (UK). The Austin Chalk of the US Gulf coast is a prolific, fractured oil reservoir that spurred widespread horizontal drilling activity.

oil sand

A porous sand layer or sand body filled with oil.

mud motor

A positive displacement drilling motor that uses hydraulic horsepower of the drilling fluid to drive the drill bit. It is used extensively in directional drilling operations.

gauge ring

A precisely machined test device, typically fabricated from steel or similar durable material, having a specified internal or external diameter. The '' '' is used to confirm the dimensional compatibility of tools and equipment that must pass through restrictions of a certain diameter

Screening

A preliminary assessment of the suitability of a reservoir for a particular process or development methodology. The assessment compares the reservoir characteristics to a number of criteria.

downhole gauge

A pressure gauge, typically run on slickline, used to measure and record downhole pressure. '''' are commonly used in assessing the downhole pressure under various flowing conditions, the basis of pressure transient analysis.

casing shoe test

A pressure test applied to the formation directly below a casing shoe. The test is generally conducted soon after drilling resumes after an intermediate casing string has been set. The purpose of the test is to determine the maximum pressures that may be safely applied without the risk of formation breakdown. The results of the test are used to design the mud program for the subsequent hole section and to set safe limits on casing shut-in or choke pressures for well-control purposes.

rotating control device (RCD)

A pressure-control device used during drilling for the purpose of making a seal around the drillstring while the drillstring rotates. This device is intended to contain hydrocarbons or other wellbore fluids and prevent their release to the atmosphere

Gas drive

A primary recovery mechanism for oil wells containing dissolved and free gas, whereby the energy of the expanding gas is used to drive the oil from the reservoir formation into the wellbore.

gasdrive

A primary recovery mechanism for oil wells containing dissolved and free gas, whereby the energy of the expanding gas is used to drive the oil from thereservoir formation into the wellbore.

drillstem test (DST)

A procedure to determine the productive capacity, pressure, permeability or extent (or a combination of these) of a hydrocarbon reservoir.

hardbanding

A process in which a wear-resistant alloy is applied to the tool joints of drillpipe or drill collars to prolong the life of oilfield tubulars. Hardbanding is applied where rotational and axial friction associated with drilling and tripping create excessive abrasive wear between drillstring and casing, or between drillstring and rock. Hard alloy overlays are applied to the points of greatest contact, typically using advanced welding techniques. Typical alloys used in this process range from ultra-wear resistant tungsten carbide, to less abrasive chromium carbide, titanium carbide and borides. Some hardbanding processes take a different approach to reducing wear in tubulars, using materials that achieve a low coefficient of friction used to protect the drillstring from abrasion.

Nitrogen injection

A process whereby nitrogen gas is injected into an oil reservoir to increase the oil recovery factor.

Off pattern well

A production or injection well that has a lateral or diagonal displacement with respect to the other wells in an injection pattern.

seal receptacle

A profiled completion component designed to accept a mating component equipped with a seal assembly. Completions are designed with '' ''' to enable the production string to be removed without removing the packer or permanent completion components.

Interfacial tension

A property of the interface between two immiscible phases, particularly in the case of two liquid phases. The Gibbs free energy per unit area of interface at fixed temperature and pressure.

thread protector

A protective sleeve or cap generally made up on the threads of tubular goods during transport and storage.

sheave

A pulley. In oilfield usage, the term usually refers to either the pulleys permanently mounted on the top of the rig (the crown blocks), or the pulleys used for running wireline tools into the wellbore.

isotropy

A quality of directional uniformity in material such that physical properties do not vary in different directions. In rocks, changes in physical properties in different directions, such as the alignment of mineral grains or the seismic velocity measured parallel or perpendicular to bedding surfaces, are forms of anisotropy. (Compare with homogeneity.)

Precipitate

A reaction by-product that can cause formation damage.

GPTS (geomagnetic polarity time scale)

A record of the onset and duration of the multitude of episodes of reversal of the Earth's magnetic polarity, or geomagnetic polarity reversals. The GPTS was developed by thorough study of rocks from around the world, during which it was observed that rocks from specific time periods contained magnetic minerals whose orientation was opposite to that of the current magnetic field. By comparing the patterns of magnetic reversals with those of rocks of known age, the approximate ages of rocks can be established. This is particularly useful for basalts of the oceanic crust, which record the Earth's magnetic field as they solidify from molten lava symmetrically about the midocean ridges. The time scale has been accurately extended back to the Upper Jurassic, the age of oldest existing oceanic crust.

geomagnetic polarity time scale

A record of the onset and duration of the multitude of episodes of reversal of the Earth's magnetic polarity, or geomagnetic polarity reversals. The GPTS was developed by thorough study of rocks from around the world, during which it was observed that rocks from specific time periods contained magnetic minerals whose orientation was opposite to that of the current magnetic field. By comparing the patterns of magnetic reversals with those of rocks of known age, the approximate ages of rocks can be established. This is particularly useful for basalts of the oceanic crust, which record the Earth's magnetic field as they solidify from molten lava symmetrically about the midocean ridges. The time scale has been accurately extended back to the Upper Jurassic, the age of oldest existing oceanic crust.

zip groove

A reduced-diameter section that has been machined at the box (up) end of a drill collar (usually a straight drill collar) so that the collar may be more easily handled with open-and-close elevators

Young-Laplace equation

A relationship describing the pressure difference across an interface between two fluids at a static, curved interface. This relationship defines the capillary pressure difference at such an interface.

platform

A relatively flat, nearly level area of sedimentary rocks in a continent that overlies or abuts the basement rocks of a craton.

horst

A relatively high-standing area formed by the movement of normal faults that dip away from each other. Horsts occur between low-standing fault blocks called graben. Horsts can form in areas of rifting or extension, where normal faults are the most abundant variety of fault.

seal

A relatively impermeable rock, commonly shale, anhydrite or salt, that forms a barrier or cap above and around reservoir rock such that fluids cannot migrate beyond the reservoir. A seal is a critical component of a complete petroleum system. The permeability of a seal capable of retaining fluids through geologic time is ~ 10-6 to 10-8 darcies.

cap rock

A relatively impermeable rock, commonly shale, anhydrite or salt, that forms a barrier or seal above and around reservoir rock so that fluids cannot migrate beyond the reservoir. It is often found atop a salt dome. The permeability of a cap rock capable of retaining fluids through geologic time is ~ 10^-6-10^-8 darcies.

caprock

A relatively impermeable rock, commonly shale, anhydrite or salt, that forms a barrier or seal above and around reservoir rock so that fluids cannot migrate beyond the reservoir. It is often found atop a salt dome. The permeability of a caprock capable of retaining fluids through geologic time is ~ 10^-6-10^-8 darcies.

graben

A relatively low-standing fault block bounded by opposing normal faults. This (used as both singular and plural) can form in areas of rifting or extension, where normal faults are the most common type of fault. Between graben are relatively high-standing blocks called horsts. A half-graben is a downdropped block bounded by a normal fault on only one side.

diapir

A relatively mobile mass that intrudes into preexisting rocks. Diapirs commonly intrude vertically through more dense rocks because of buoyancy forces associated with relatively low-density rock types, such as salt, shale and hot magma, which form diapirs. The process is known as diapirism. By pushing upward and piercing overlying rock layers, diapirs can form anticlines, salt domes and other structures capable of trapping hydrocarbons. Igneous intrusions are typically too hot to allow the preservation of preexisting hydrocarbons.

flow coupling

A relatively short, heavy-walled completion component installed in areas where turbulence is anticipated. The additional wall thickness prevents early failures due to erosion in the turbulent flowarea. '' ''' are typically installed above and below completion components, such as landing nipples, that may affect the flow.

sweep pill

A relatively small volume of viscous fluid, typically a carrier gel, that is circulated to sweep, or remove, debris or residual fluids from the circulation system.

Cat Line

A relatively thin cable used with other equipment to move small rig and drill string components and to provide tension on the tongs for tightening or loosening threaded connections.

cat line

A relatively thin cable used with other equipment to move small rig and drillstring components and to provide tension on the tongs for tightening or loosening threaded connections.

pipe dope

A specially formulated blend of lubricating grease and fine metallic particles that prevents thread galling (a particular form of metal-to-metal damage) and seals the roots of threads.

cement squeeze

A remedial cementing operation designed to force cement into leak paths in wellbore tubulars. The required squeeze pressure is achieved by carefully controlling pump pressure. ''' operations may be performed to repair poor primary cement jobs, isolate perforations or repair damagedcasing or liner.

cement bond log OR cement evaluation log

A representation of the integrity of the cement job, especially whether the cement is adhering solidly to the outside of the casing. It is typically obtained from one of a variety of sonic-type tools.

Cement Bond Log

A representation of the integrity of the cement job, especially whether the cement is adhering solidly to the outside of the casing. The log is typically obtained from one of a variety of sonic-type tools

cement evaluation log

A representation of the integrity of the cement job, especially whether the cement is adhering solidly to the outside of the casing. The log is typically obtained from one of a variety of sonic-type tools. The newer versions along with their processing software, can give detailed, 360-degree representations of the integrity of the cement job, whereas older versions may display a single line representing the integrated integrity around the casing

Caliper Log

A representation of the measured diameter of a borehole along its depth. These are usually measured mechanically, with only a few using sonic devices.

caliper log

A representation of the measured diameter of a borehole along its depth. These logs are usually measured mechanically, with only a few using sonic devices. The tools measure diameter at a specific chord across the well.

conventional reservoir

A reservoir in which buoyant forces keep hydrocarbons in place below a sealing caprock. Reservoir and fluid characteristics of conventional reservoirs typically permit oil or natural gas to flow readily into wellbores. The term is used to make a distinction from shale and other unconventional reservoirs, in which gas might be distributed throughout the reservoir at the basin scale, and in which buoyant forces or the influence of a water column on the location of hydrocarbons within the reservoir are not significant.

gas injection

A reservoir maintenance or secondary recovery method that uses injected gas to supplement thepressure in an oil reservoir or field. In most cases, a field will incorporate a planned distribution of '' '' wells to maintain reservoir pressure and effect an efficient sweep of recoverable liquids.

pay

A reservoir or portion of a reservoir that contains economically producible hydrocarbons. The term derives from the fact that it is capable of "paying" an income. Pay is also called pay sand or pay zone. The overall interval in which pay sections occur is the gross pay; the smaller portions of the gross pay that meet local criteria for pay (such as minimum porosity, permeability and hydrocarbon saturation) are net pay.

waterdrive

A reservoir-drive mechanism whereby the oil is driven through the reservoir by an active aquifer. As the reservoir depletes, the water moving in from the aquifer below displaces the oil until the aquifer energy is expended or the well eventually produces too much water to be viable.

varve

A rhythmic sequence of sediments deposited in annual cycles in glacial lakes. Light-colored, coarse summer grains are deposited by rapid melting of the glacier. The summer layers grade upward to layers of finer, dark winter grains of clay minerals or organic material that are deposited slowly from suspension in quiet water while streams and lakes are icebound. Varves are useful to the study of geochronology because they can be counted to determine the absolute age of some Pleistocene rocks of glacial origin.

standpipe

A rigid metal conduit that provides the high-pressure pathway for drilling mud to travel approximately one-third of the way up the derrick, where it connects to a flexible high-pressure hose (kelly hose).

dolostone

A rock composed chiefly (> 90%) of dolomite. The rock is sometimes called dolomite, but dolostone is preferable to avoid ambiguity between the mineral and rock names. Replacement dolomite that forms soon after deposition is typically fine-grained and preserves original sedimentary structures. Recrystallization late in diagenesis produces coarser grained dolomite, destroys sedimentary structures and results in higher porosity.

source rock

A rock rich in organic matter which, if heated sufficiently, will generate oil or gas. Typically these are usually shales or limestones and contain about 1% organic matter and at least 0.5% total organic carbon (TOC), although a rich source rock might have as much as 10% organic matter. Rocks of marine origin tend to be oil-prone, whereas terrestrial source rocks (such as coal) tend to be gas-prone. Preservation of organic matter without degradation is critical to creating a good source rock, and necessary for a complete petroleum system. Under the right conditions, source rocks may also be reservoir rocks, as in the case of shale gas reservoirs.

Polish rod

A rod which connects the Sucker rods inside the wellbore to the bridle and Horsehead at the top of the SRP surface assembly. This rod is usally made up of variable lengths between 6-20 feet, while the sucker rods are typically 30 ft in length. The main use of this rod is for length adjustment in installation and for good sealing.

float shoe

A rounded profile component attached to the downhole end of a casing string. An integral check valve in the '' '''prevents reverse flow, or U-tubing, ofcement slurry from the annulus into the casing or flow of wellbore fluids into the casing string as it is run. The '' ''' also guides the casing toward the center of the hole to minimize hitting rock ledges or washouts as the casing is run into the wellbore. The '' ''' reduces hook weight. With controlled or partial fill-up as the string is run, the casing string can be floated into position, avoiding the need for the rig to carry the entire weight of the casing string.

cementing plug

A rubber plug used to separate the cement slurry from other fluids, reducing contamination and maintaining predictable slurry performance.

cementing plug

A rubber plug used to separate the cement slurry from other fluids, reducing contamination and maintaining predictable slurry performance. Two types of cementing plug (the top plug and the bottom plug) are typically used on a cementing operation.

subsurface safety valve (SSSV)

A safety device installed in the upper wellbore to provide emergency closure of the producing conduits in the event of an emergency. Two types of ' ' ' ' are available: surface-controlled and subsurface controlled. In each case, the safety-valve system is designed to be fail-safe, so that the wellbore is isolated in the event of any system failure or damage to the surfaceproduction-control facilities.

gravel pack

A sand-control method used to prevent production of formation sand. In gravel pack operations, a steel screen is placed in the wellbore and the surroundingannulus packed with prepared gravel of a specific size designed to prevent the passage of formation sand. The primary objective is to stabilize the formation while causing minimal impairment to well productivity.

wellbore diagram

A schematic diagram that identifies the main completion components installed in a wellbore.

geologist

A scientist trained in the study of the Earth. In the petroleum industry, geologists perform a wide variety of functions, but typically generate prospects and interpret data such as maps, well logs, outcrops, cuttings, core samples and seismic data.

blast joint

A section of heavy walled tubing that is placed across any perforated interval through which the production tubing must pass, such as may be required in multiple zone completions. In addition to being heavier than normal completion components, the wall of a ''' is often treated to resist the jetting action that may result in the proximity of the perforations.

tie back liner

A section of liner that is run from a liner hanger back to the wellhead after the initial liner and hanger system have been installed and cemented. A '' '' '' may be required to provide the necessary pressure capacity during a flow-test period or for special treatments, and is typically not cemented in place. In some cases, a '' '' '' will be installed as a remedial treatment when the integrity of the intermediate casing string is in doubt.

chert

A sedimentary rock and a variety of quartz made of extremely fine-grained, or cryptocrystalline, silica, also called chalcedony. The silica might be of organic origin, such as from the internal structures of sponges called spicules, or inorganic origin, such as precipitation from solution. The latter results in the formation of flint. Chert can form beds, but is more common as nodules in carbonate rocks.

jackup OR jackup rig

A self-contained combination drilling rig and floating barge, fitted with long support legs that can be raised or lowered independently of each other.

estuary

A semi-enclosed coastal environment of deposition in which a river mouth permits freshwater to contact and mix with seawater.

Choke Manifold

A set of high-pressure valves and associated piping that usually includes at least two adjustable chokes, arranged such that one adjustable choke may be isolated and taken out of service for repair and refurbishment while well flow is directed through the other one.

choke manifold

A set of high-pressure valves and associated piping that usually includes at least two adjustable chokes, arranged such that one adjustable choke may be isolated and taken out of service for repair and refurbishment while well flow is directed through the other one.

Microemulsion

A thermodynamically stable emulsion consisting of a mixture of oil, water and surfactant.

block

A set of pulleys used to gain mechanical advantage in lifting or dragging heavy objects. There are two large *** on a drilling rig, the crown *** and the traveling ***. Each has several sheaves that are rigged with steel drilling cable or line such that the traveling block may be raised (or lowered) by reeling in (or out) a spool of drilling line on the drawworks.

Paraffin control

A set of techniques used to prevent or considerably reduce paraffin deposition.

BOP Stack

A set of two or more BOPs used to ensure pressure control of a well. A typical configuration might consist of one to six ram-type preventers and, optionally, one or two annular-type preventers. It also has the ram preventers on the bottom and the annular preventers at the top. The configuration of preventers is optimized to provide maximum pressure integrity, safety and flexibility in the event of a well control incident.

hydraulic set

A setting or operating method that uses hydraulic force applied through the tubing or running string to activate a downhole tool. In many cases a drop ball, which lands in a profiled seat, will be used to shift the setting or activation mechanism at predetermined pressures.

casing swage

A short crossover joint used between two sizes or specifications of casing. A ''' is an adapter that enables a temporary circulating line to be rigged to the top of the casing string, allowingcirculation of fluids to help properly locate the casing string.

lifting sub

A short drillstring component that is temporarily connected to the top of a tool assembly that is to be lifted vertically, such as when running or retrieving a tool string.

saver sub

A short length of drill collar that has male threads on one end and female on the other. It is screwed onto the bottom of the kelly or topdrive and onto the rest of the drillstring.

casing coupling

A short length of pipe used to connect two joints of casing.

Casing Coupling

A short length of pipe used to connect two joints of casing. It has internal threads (female threadform) machined to match the external threads (male threadform) of the long joints of casing.

shear pin

A short piece of brass or steel that is used to retain sliding components in a fixed position until sufficient force is applied to break the pin. Once the pin is sheared, the components can then move to operate or function the tool

blank pipe

A short section of plain tubing used to separate or space-out specialized components in a completionassembly. '''' is commonly used in sand control completions where intervals of screen are separated by short sections of blank pipe. The term is also used to describe unperforated sections ofcasing or liner.

conductor pipe

A short string of large-diameter casing set to support the surface formations. The conductor pipe is typically set soon after drilling has commenced since the unconsolidated shallow formations can quickly wash out or cave in. Where loose surface soil exists, the ''' may be driven into place before the drilling commences.

cross over

A short subassembly used to enable two components with different thread types or sizes to be connected.

tubing joint

A single length of the pipe that is assembled to provide a conduit through which the oil or gas will be produced from a wellbore.

multiple completion

A single wellbore having tubulars and equipment that enable production from two or more reservoirzones.

dual completion

A single wellbore having tubulars and equipment that enable production from two segregated zones. In most cases, two tubing strings will be used to provide the necessary level of control and safety for the fluids from both zones. However, in some simple ''' '''', the second or upper zone is produced up the tubing-casing annulus.

rabbit

A slang term for an internal drift diameter gauge typically used to check casing or tubing joints before they are picked up and run into the wellbore.

microannulus

A small gap that can form between the casing or liner and the surrounding cement sheath, most commonly formed by variations in temperature or pressure during or after the cementing process.

keyseat

A small-diameter channel worn into the side of a larger diameter wellbore. This can be the result of a sharp change in direction of the wellbore (a dogleg), or if a hard formation ledge is left between softer formations that enlarge over time. In either case, the diameter of the channel is typically similar to the diameter of the drillpipe.

injection line

A small-diameter conduit that is run alongside production tubulars to enable injection of inhibitors or similar treatments during production. Conditions such as high hydrogen sulfide [H2S] concentrations or severe scale deposition can be counteracted by injection of treatment chemicals and inhibitors during production.

control line

A small-diameter hydraulic line used to operate downhole completion equipment such as the surface controlled subsurface safety valve (SCSSV). Most systems operated by '' operate on a fail-safe basis. In this mode, the ''' remains pressurized at all times. Any leak or failure results in loss of control line pressure, acting to close the safety valve and render the well safe.

velocity string

A small-diameter tubing string run inside the production tubing of a well as a remedial treatment to resolve liquid-loading problems. As the reservoir pressure in a gas well depletes, there may be insufficient velocity to transport all liquids from the wellbore. In time these liquids accumulate and impair production. Installing a '' ''' reduces the flow area and increases the flow velocity to enable liquids to be carried from the wellbore.

diatomite

A soft, silica-rich sedimentary rock comprising diatom remains that forms most commonly in lakes and deep marine areas. Diatomite can form an excellent reservoir rock. The Belridge diatomite in the San Joaquin basin, California, USA, is a prolific oil-producing formation.

asphalt

A solid or nearly solid form of bitumen that can melt upon heating and contains impurities such as nitrogen, oxygen and sulfur. Asphalt forms naturally when the light components or volatiles of petroleum have been removed or evaporated.

completion fluid

A solids-free liquid used to "complete" an oil or gas well. This fluid is placed in the well to facilitate final operations prior to initiation of production, such as setting screens production liners, packers, downhole valves or shooting perforations into the producing zone. The fluid is meant to control a well should downhole hardware fail, without damaging the producing formation or completion components. '' are typically brines (chlorides, bromides and formates), but in theory could be any fluid of proper density and flow characteristics. The fluid should be chemically compatible with the reservoirformation and fluids, and is typically filtered to a high degree to avoid introducing solids to the near-wellbore area. Seldom is a regular drilling fluid suitable for completion operations due to its solids content, pH and ionic composition. Drill-in fluids can, in some cases, be suitable for both purposes.

tubing puncher

A special perforating gun, or charge, that is designed for limited penetration to allow an inner tubing orcasing string to be perforated without damaging a surrounding outer string. These guns often are used in remedial or workover operations in which downhole communication devices, such as sliding sleeves, cannot be opened to allow circulation of well-kill fluids.

Bit Breaker

A special tool used by the rig crew to prevent the drill bit from turning while the bit sub on top of it is tightened or loosened.

crossover service tool

A specialized tool, frequently used in gravel-pack operations, that enables the circulation of the treatment fluid (slurry) from the internal flow path of the tool string into the annulus area to be packed. The returned carrier fluid enters the internal flow path at the base of the tool before crossing over to the annulus above the packer assembly, isolating the annulus.

slant hole rig

A specially designed drilling rig capable of drilling directional wells.

tie back packer

A specially designed packer assembly used in conjunction with a tie-back liner. The '' '' '' can be integral to the original liner hanger, or if the tie-back is a remedial treatment, it can be a separate component set above the liner hanger.

corrosion-resistant alloy (CRA)

A specially formulated material used for completion components in wells likely to present corrosionproblems. ''''''' can be formulated for a wide range of aggressive wellbore conditions. However, cost generally determines the viability of any particular completion design. Alloys with a high chrome content are commonly used for tubing strings.

perforating fluid

A specially prepared fluid placed in the wellbore over the interval to be perforated. The ideal fluid is clean and solids-free (filtered), and will not react to cause damaging by-products on contact with thereservoir formation. Perforating in a dirty fluid may result in significant permeability damage that is difficult to treat and remove.

craton

A stable area of continental crust that has not undergone much plate tectonic or orogenic activity for a long period. A craton includes a crystalline basement of commonly Precambrian rock called a shield, and a platform in which flat-lying or nearly flat-lying sediments or sedimentary rock surround the shield. A commonly cited example of a craton is the Canadian Shield.

Spinning-drop tensiometer

A standard laboratory instrument to measure interfacial tension. The method is particularly applicable to values of interfacial tension below 1 mN/m and especially below 10-2 mN/m, as may occur when employing surfactants for enhanced oil recovery.

Pendant-drop tensiometer

A standard laboratory instrument used to measure interfacial tension.

escape line OR Geronimo line

A steel cable attached to the rig derrick or mast near the work platform for the derrickman. This cable is anchored at surface level (on a vessel or the Earth) away from the mast in a loose catenary profile, and fitted with a handle and hand brake that is stored at the top. It provides a rapid escape path for the derrickman should well conditions or massive mechanical failure warrant.

skid

A steel frame on which portable equipment is mounted to facilitate handling with cranes or flatbed trucks.

hydraulic fracturing

A stimulation treatment routinely performed on oil and gas wells in low-permeability reservoirs. Specially engineered fluids are pumped at high pressure and rate into the reservoir interval to be treated, causing a vertical fracture to open. The wings of the fracture extend away from the wellbore in opposing directions according to the natural stresses within the formation. Proppant, such as grains of sand of a particular size, is mixed with the treatment fluid to keep the fracture open when the treatment is complete. Hydraulic fracturing creates high-conductivity communication with a large area of formation and bypasses any damage that may exist in the near-wellbore area.

rathole

A storage place for the kelly, consisting of an opening in the rig floor fitted with a piece of casing with an internal diameter larger than the outside diameter of the kelly, but less than that of the upper kelly valve so that the kelly may be lowered into the rathole until the upper kelly valve rests on the top of the piece of casing.

tapered string

A string comprising tubing or components of varying size or dimension. A tapered production string may be configured with larger OD tubing joints in the upper wellbore area to optimize the hydraulic performance of the string. Although a tapered coiled tubing string will have the same tubing outside diameter throughout, the upper portion of the string may have a greater wall thickness to support the load of the string below.

Tapered String or Combination String

A string of drillpipe or casing that consists of two or more sizes or weights.

tapered string

A string of drillpipe or casing that consists of two or more sizes or weights.

Oil mining

A strip-mining process involving the removal and subsequent processing of tar sand from shallow reservoirs containing heavy, viscous oil.

horizontal drilling

A subset of the more general term "directional drilling," used where the departure of the wellbore from vertical exceeds about 80 degrees.

reservoir

A subsurface body of rock having sufficient porosity and permeability to store and transmit fluids. Sedimentary rocks are the most common reservoir rocks because they have more porosity than most igneous and metamorphic rocks and form under temperature conditions at which hydrocarbons can be preserved. A reservoir is a critical component of a complete petroleum system.

abnormal pressure

A subsurface condition in which the pore pressure of a geologic formation exceeds or is less than the expected, or normal, formation pressure. When impermeable rocks such as shales are compacted rapidly, their pore fluids cannot always escape and must then support the total overlying rock column, leading to abnormally high formation pressures. Excess pressure, called overpressure or geopressure, can cause a well to blowout or become uncontrollable during drilling. Severe underpressure can cause the drillpipe to stick to the underpressured formation.

oil pool

A subsurface oil accumulation. An oil field can consist of one or more of these or distinct reservoirs within a single large trap. The term "pool" can create the erroneous impression that oil fields are immense caverns filled with oil, instead of rock filled with small oil-filled pores.

dry rock

A subsurface rock that lacks contact with aquifers or meteoric water within the Earth.

drilling break

A sudden increase in the rate of penetration during drilling. When this increase is significant (two or more times the normal speed, depending on local conditions), it may indicate a formation change, a change in the pore pressure of the formation fluids, or both. It is commonly interpreted as an indication of the bit drilling sand (high-speed drilling) rather than shale (low-speed drilling).

back up ring

A supporting ring used with an O-ring, or similar seal, to prevent extrusion of the seal material under high differential pressures or excess wear under dynamic sealing conditions

back-up ring

A supporting ring used with an O-ring, or similar seal, to prevent extrusion of the seal material under high differential pressures or excess wear under dynamic sealing conditions.

volcano

A surface feature of the Earth that allows magma, ash and gas to erupt. The vent can be a fissure or a conical structure.

show

A surface observation of hydrocarbons, usually observed as florescent liquid on cuttings when viewed with an ultraviolet or black light (for oil) or increased gas readings from the mud logger's gas-detection equipment (for gas).

joint

A surface of breakage, cracking or separation within a rock along which there has been no movement parallel to the defining plane. The usage by some authors can be more specific: When walls of a fracture have moved only normal to each other, the fracture is called a joint.

sequence boundary

A surface that separates older sequences from younger ones, commonly an unconformity (indicating subaerial exposure), but in limited cases a correlative conformable surface. A sequence boundary is an erosional surface that separates cycles of deposition.

angular unconformity

A surface that separates younger strata from eroded, dipping, older strata and represents a gap in the geologic record.

tubing grade

A system of classifying the material specifications for steel alloys used in the manufacture of tubing.

casing grade

A system of identifying and categorizing the strength of casing materials.

GPS

A system of numerous Earth-orbiting satellites that can be used to determine the location (latitude, longitude and elevation) of a receiver or station on the Earth within about 2 m [6 ft]. Fixed receivers on Earth can be used to determine the relative motions of fault blocks and lithospheric plates. Hand-held receivers can be used for producing accurate geologic maps, acquiring navigation data for 3D seismic surveys, and positioning wells in the field.

tubing seal assembly

A system of seals arranged on the component that engages in a sealbore to isolate the production-tubing conduit from the annulus.

seal assembly

A system of seals arranged on the component that engages in a sealbore to isolate the production-tubing conduit from the annulus. is typically longer than the sealbore to enable some movement of the components while maintaining an efficient seal.

guide shoe OR shoe

A tapered, often bullet-nosed piece of equipment often found on the bottom of a casing string. The device guides the casing toward the center of the hole and minimizes problems associated with hitting rock ledges or washouts in the wellbore as the casing is lowered into the well. The outer portions are made from steel. The inside (including the taper) is generally made of cement or thermoplastic

microseismic monitoring

A technique to track the propagation of a hydraulic fracture as it advances through a formation. Microseisms are detected, located, and displayed in time for scientists and engineers to approximate the location and propagation of the hydraulic fracture.

Blind Ram

A thick, heavy steel component of a conventional ram blowout preventer. In a normal pipe ram, the two blocks of steel that meet in the center of the wellbore to seal the well have a hole through which the pipe fits. It has no space for pipe and is instead blanked off in order to be able to close over a well that does not contain a drillstring

Sludge

A thick, viscous emulsion containing oil, water, sediment and residue that forms because of the incompatibility of certain native crude oils and strong inorganic acids used in well treatments.

hydraulic fracture monitoring

A technique to track the propagation of a hydraulic fracture as it advances through a formation. Microseisms are detected, located, and displayed in time for scientists and engineers to approximate the location and propagation of the hydraulic fracture. Software provides modeling, survey design, microseismic detection and location, uncertainty analysis, data integration, and visualization forinterpretation. Computer imagery is used to monitor the activity in 3D space relative to the location of the fracturing treatment. The monitored activities are animated to show progressive fracture growth and the subsurface response to pumping variations. When displayed in real time, the microseismic activity allows one to make changes to the stimulation design to ensure optimal reservoir contact. Also known as microseismic monitoring, this technique delivers information about the effectiveness of the stimulation of a reservoir that can be used to enhance reservoir development in shale gas completions.

alidade

A telescopic surveying device used to construct surface topographic and geologic maps in the field. This device is mounted on a plane table, which has a sheet of paper on which to draw the map, and an object or location is sighted through the alidade. The edge of the alidade is aligned in the azimuthal direction of the object or location. The vertical angle from which elevation of the location can be calculated is measured using the calibrated arc of the alidade.

slip joint OR travel joint

A telescoping joint at the surface in floating offshore operations that permits vessel heave (vertical motion) while maintaining a riser pipe to the seafloor.

calcium carbonate plug

A temporary plug formulated with graded granules or flakes of calcium carbonate that are generally circulated into place as a slurry and allowed to settle out. ''' commonly are used to isolate lower production zones, either to enable a column of well control fluid to be placed, or to provide some protection for a lower zone while treating upper zones. Because of their high reaction rate with hydrochloric acid, ''' are easily removed using common acidizing materials and equipment.

expendable plug

A temporary plug, inserted in the completion assembly before it is run, to enable pressure testing of the completed string. With the operation complete, the '' '' can be pumped out of the assembly, thereby avoiding a separate retrieval run.

salt plug

A temporary plugging agent comprising graded granules of salt that form a physical or hydraulic barrier. The different grain sizes are prepared as a slurry for placement, then allowed to settle into a plug. The resulting plug typically provides good mechanical and hydraulic strength to enable safe treatment of an adjacent zone.

hard rock

A term applied to igneous and metamorphic rocks that are distinguished from sedimentary rocks because they are typically more difficult to disaggregate. Well cemented sedimentary rocks are sometimes described as being hard, but are usually called soft rock. The term can be used to differentiate between rocks of interest to the petroleum industry (soft rocks) and rocks of interest to the mining industry (hard rocks).

casing pressure

A term used in well-control operations, typically during the drilling or workover phases of a well, to describe the pressure in the drillpipe or tubing annulus.

commingled flow

A term used to describe the flow pattern where two or more fluid phases may be present in a relatively even distribution. The flow rate and conduit geometry may cause an apparent mixing of the phases. However, if the flow characteristics are changed through flow rate or conduit geometry, fluid separation may occur. Fine solids also may be entrained in a commingled flow. ''' may also describe the production of fluid from two or more separate zones through a single conduit.

Carbide Lag Test

A test performed by the mudlogger or wellsite geologist, used to calculate sample lag. The lag period can be measured as a function of time or pump strokes

carbide lag test

A test performed by the mudlogger or wellsite geologist, used to calculate sample lag. The lag period can be measured as a function of time or pump strokes. Acetylene is commonly used as a tracer gas for this purpose.

step rate test

A test performed in preparation for a hydraulic fracturing treatment in which an injection fluid is injected for a defined period in a series of increasing pump rates. The resulting data are used to identify key treatment parameters of the fracturing operation, such as the pressure and flow rates required to successfully complete the treatment.

flow check

A test performed to ensure stable well conditions or the integrity of a plug, valve or flow-control device. In most cases, the ''' ''' involves observing stable fluid levels or conditions for a prescribed period.

leak off test (LOT) OR pressure integrity test (PIT)

A test to determine the strength or fracture pressure of the open formation, usually conducted immediately after drilling below a new casing shoe. During the test, the well is shut in and fluid is pumped into the wellbore to gradually increase the pressure that the formation experie

Steam assisted gravity drainage (SAGD).

A thermal production method for heavy oil that pairs a high-angle injection well with a nearby production well drilled along a parallel trajectory. Steam is injected into the upper well, heats the oil and reduces its viscosity. Oil then drains into the lower well under the influence of gravity.

slickline

A thin nonelectric cable used for selective placement and retrieval of wellbore hardware, such as plugs, gauges and valves located in sidepocket mandrels. Valves and sleeves can also be adjusted using slickline tools.

buttress thread

A thread profile used on casing or liner tubulars. ''' are square-cut and create a hydraulic seal through the interference fit of the mating threads.

swage

A threaded adapter used to connect a circulating line to a casing or tubing string. A casing or tubing ''' generally is required as a contingency option to enable any obstruction or fill to be circulated clear during the running process.

collar

A threaded coupling used to join two lengths of pipe such as production tubing, casing or liner. The type of thread and style of ''' varies with the specifications and manufacturer of the tubing.

overthrust

A thrust fault having a relatively large lateral displacement.

diamond bit

A tool for drilling rock that works by scraping industrial grade diamonds against the bottom of the hole. The diamonds are embedded into the metal structure (usually a sintered or powdered carbide basematrix) during the manufacture.

bottomhole sampler

A tool or assembly used to retrieve samples of fluids or fill material from the wellbore. Used as a treatment design aid, the retrieved samples can be checked for compatibility with the selected treatment fluid to verify performance or identify any undesirable reactions.

basket sub

A tool run into the wellbore to retrieve junk from the bottom of the hole.

junk basket OR basket sub OR junk sub

A tool run into the wellbore to retrieve junk from the bottom of the hole.

mill

A tool that grinds metal downhole. It is usually used to remove junk in the hole or to grind away all or part of a casingstring.

stimulation

A treatment performed to restore or enhance the productivity of a well. These treatments fall into two main groups, hydraulic fracturing treatments and matrix treatments. Fracturing treatments are performed above the fracture pressure of the reservoir formation and create a highly conductive flow path between the reservoir and the wellbore. Matrix treatments are performed below the reservoir fracture pressure and generally are designed to restore the natural permeability of the reservoir following damage to the near-wellbore area

Tubing displacement

A type of batch-treating technique used in corrosion control in which a batch of corrosion inhibitor is displaced through the tubing to the bottom of the well. Also called a kiss-squeeze.

Standard batch

A type of batch-treating technique used in corrosion control. The batch of corrosion inhibitor is displaced through the annulus to the bottom of the well. Once the inhibitor is at the bottom, it is circulated up the tubing and returned back into the annulus, leaving a considerable amount of inhibitor in the annulus for further circulation.

Ringworm corrosion

A type of bimetallic corrosion. The corrosion has the shape of a ring and is located a few inches from the pipe upset. The ring can either be very smooth or have severe pitting.

back-pressure valve

A type of check valve, typically installed in the tubing hanger, to isolate the production tubing. The '''' is designed to hold pressure from below yet enable fluids to be pumped from above, as may be required for well-control purposes.

back pressure valve

A type of check valve, typically installed in the tubing hanger, to isolate the production tubing. The back-pressure valve is designed to hold pressure from below yet enable fluids to be pumped from above, as may be required for well-control purposes.

kaolinite

A type of clay mineral from the kaolin group that forms through the weathering of feldspar and mica group minerals. Unlike some clay minerals like montmorillonite, kaolinite is not prone to shrinking or swelling with changes in water content.

Pitting

A type of corrosion in which there is loss of metal in localized areas.

Hydrogen induced failures

A type of corrosion produced when a metal absorbs hydrogen atoms. This phenomenon can cause undesirable effects such as blistering, cracking, methane formation above 400F and hydrogen embrittlement.

Induced particle plugging

A type of damage in which foreign particles injected during normal well operations, such as drilling, completion, workover, stimulation or enhanced recovery, block the near-wellbore formation, reducing well productivity.

retrievable bridge plug

A type of downhole isolation tool that may be unset and retrieved from the wellbore after use, such as may be required following treatment of an isolated zone.

compression-set packer

A type of downhole packer that is activated or set by applying compressive force to the packer assembly. In most cases, this is achieved with set-down weight from the running string, which is controlled by the driller or operatorobserving the weight indicator on the rig or coiled tubing unit.

heavyweight drillpipe (HWDP)

A type of drillpipe whose walls are thicker and collars are longer than conventional drillpipe. It tends to be stronger and has higher tensile strength than conventional drillpipe, so it is placed near the top of a long drillstring for additional support.

reverse fault

A type of fault formed when the hanging wall fault block moves up along a fault surface relative to the footwall. Such movement can occur in areas where the Earth's crust is compressed. A thrust fault, sometimes called an overthrust if the displacement is particularly great, is a reverse fault in which the fault plane has a shallow dip, typically much less than 45o.

normal fault

A type of fault in which the hanging wall moves down relative to the footwall, and the fault surface dips steeply, commonly from 50º to 90º. Groups of normal faults can produce horst and graben topography, or a series of relatively high- and low-standing fault blocks, as seen in areas where the crust is rifting or being pulled apart by plate tectonic activity. A growth fault is a type of normal fault that forms during sedimentation and typically has thicker strata on the downthrown hanging wall than the footwall.

strike-slip fault

A type of fault whose surface is typically vertical or nearly so. The motion along a strike-slip fault is parallel to the strike of the fault surface, and the fault blocks move sideways past each other. A strike-slip fault in which the block across the fault moves to the right is described as a dextral strike-slip fault. If it moves left, the relative motion is described as sinistral. Local deformation near bends in strike-slip faults can produce pull-apart basins and grabens. Flower structures are another by-product of strike-slip faults. A wrench fault is a type of strike-slip fault in which the fault surface is nearly vertical.

turnkey

A type of financing arrangement for the drilling of a wellbore that places considerable risk and potential reward on the drilling contractor. Under such an arrangement, the drilling contractor assumes full responsibility for the well to some predetermined milestone such as the successful running of logs at the end of the well, the successful cementing of casing in the well or even the completion of the well.

positive displacement pump

A type of fluid pump in which the displacement volume of the pump is fixed for each rotation of the pump. Generally associated with high-pressure applications and commonly used in drilling operations tocirculate the drilling fluid and in a range of oil and gas well treatments, such as cementing, matrix treatments and hydraulic fracturing.

positive displacement pump

A type of fluid pump in which the displacement volume of the pump is fixed for each rotation of the pump. Generally associated with high-pressure applications, '' '' '' are commonly used in drilling operations to circulate the drilling fluid and in a range of oil and gas well treatments, such ascementing, matrix treatments and hydraulic fracturing.

similar fold

A type of fold in which the thickness of the layers remains constant when measured parallel to the axial surface and the layers have the same wave shape, but the thickness along each layer varies. The folded layers tend to be thicker in the hinge of the fold and thinner along the limbs of the fold.

pyrolysis

A type of geochemical analysis in which a rock sample is subject to controlled heating in an inert gas to or past the point of generating hydrocarbons in order to assess its quality as a source rock, the abundance of organic material in it, its thermal maturity, and the quality of hydrocarbons it might generate or have generated. Pyrolysis breaks large hydrocarbon molecules into smaller molecules. This process is used to determine the quality of shale as a source rock and is instrumental in evaluating shale gas plays.

unconformity trap

A type of hydrocarbon trap whose closure is controlled by the presence of an unconformity. There is disagreement about whether unconformity traps are structural or stratigraphic traps.

Hydrogen blistering

A type of hydrogen-induced failure produced when hydrogen atoms enter low-strength steels that have macroscopic defects, such as laminations.

Reverse combustion

A type of in-situ combustion in which the burning front moves in an opposite direction to the injected air.

Scale inhibitor squeeze

A type of inhibition treatment used to control or prevent scale deposition.

selective nipple

A type of landing nipple designed to be run in a series throughout the wellbore. Two basic typesmay be encountered, a nipple series in which the nipple design or profile determines the selectivity and one in which the running tool is used to find the target nipple.

inside blowout preventer

A valve in the drillstring that may be used to prevent the well from flowing uncontrollably up the drillstring.

collar lock

A type of lock designed to be set in the recess of a tubing collar. ''' are compatible only with conventional thread connections where a space exists between the two tubing joints. Premium tubing grades have flush internal surfaces with no space to enable setting of the retaining dogs.

J slot

A type of mechanism commonly used in the setting and unsetting of downhole tools and equipment such as packers. Most conventional downhole tools operate by upward or downward movement, rotation, or a combination of both.

cataclasite

A type of metamorphic rock with shearing and granulation of minerals caused by high mechanical stress during faulting or dynamic metamorphism, typically during episodes of plate tectonic activity.

synthetic fault

A type of minor fault whose sense of displacement is similar to its associated major fault. Antithetic-synthetic fault sets are typical in areas of normal faulting.

growth fault

A type of normal fault that develops and continues to move during sedimentation and typically has thicker strata on the downthrown, hanging wall side of the fault than in the footwall. Growth faults are common in the Gulf of Mexico and in other areas where the crust is subsiding rapidly or being pulled apart.

Organic acid

A type of organic fluid, such as acetic or formic acid, used in oil and gas well-stimulation treatments.

openhole packer

A type of packer designed for use in openhole applications such as drillstem testing. Are typically configured with one large element that can be deformed easily to contact the unevenformation surface, yet retain strength and sufficient integrity to withstand the anticipated differential pressures.

hookwall packer

A type of packer than utilizes an assembly of friction blocks and slips to set and anchor the packer on thecasing or liner wall. '''' '''' generally are run on tubing or drillpipe and typically require some rotation of the packer assembly to activate or set the packer slips. Subsequent application of tension or compression, depending on packer design, will set the packer elements.

retrievable packer

A type of packer that is run and retrieved on a running string or production string, unlike a permanent production packer that is set in the casing or linerbefore the production string is run.

tension-set packer

A type of packer that is set by applying tension to the running string. These packers are less common than compression-set packers due to the potential difficulties associated with retrieval. However, in applications where there is insufficient string weight to set a compression packer, a '' '' is a useful option.

inflatable packer

A type of packer that uses an inflatable bladder to expand the packer element against the casing or wellbore. In preparation for setting the packer, a drop ball or series of tubing movements are generally required, with the hydraulic pressure required to inflate the packer provided by carefully applying surface pump pressure. Inflatable packers are capable of relatively large expansion ratios, an important factor inthrough-tubing work where the tubing size or completion components can impose a significant size restriction on devices designed to set in the casing or liner below the tubing.

hydraulic packer

A type of packer used predominantly in production applications. This device typically is set using hydraulic pressure applied through the tubing string rather than mechanical force applied by manipulating the tubing string.

Chain Tongs

A type of pipe wrench used for hand-tightening various threaded connections around the rigsite. It consists of a handle, a set of gripping die teeth, a length of flat chain and a hooking slot where the chain may be adjusted to fit the pipe.

chain tongs

A type of pipe wrench used for hand-tightening various threaded connections around the rigsite. It consists of a handle, a set of gripping die teeth, a length of flat chain and a hooking slot where the chain may be adjusted to fit the pipe.

sealbore packer

A type of production packer that incorporates a sealbore that accepts a seal assembly fitted to the bottom of the production tubing. The '' ''' is often set on wireline to enable accurate depthcorrelation. For applications in which a large tubing movement is anticipated, as may be due to thermal expansion, the '' '' and seal assembly function as a slip joint.

jet pump

A type of pump that operates on the principle of a high-pressure fluid jet and the venturi effect it creates. These pumps are relatively inefficient but can tolerate a wide range of operating conditions, including easily handling sand-laden or abrasive fluids.

Gas cap drive

A type of reservoir-drive mechanism in which the energy for the transport and production of reservoir fluids is provided by the expansion of gas in the gas cap.

Solution gas drive

A type of reservoir-drive mechanism in which the energy for the transport and production of reservoir fluids is provided by the gas dissolved in the liquid.

solution gas drive

A type of reservoir-drive system in which the energy for the transport and production of reservoir fluids is derived from the gas dissolved in the fluid. As reservoir fluids enter the wellbore, changing pressureconditions cause the gas to break from solution to create a commingled flow of gas and liquid that aids production.

thrust fault

A type of reverse fault in which the fault plane has a very shallow dip, typically much less than 45o. The hanging wall fault block moves up the fault surface relative to the footwall. In cases of considerable lateral movement, the fault is described as an overthrust fault. Thrust faults can occur in areas of compression of the Earth's crust.

wireline retrievable safety valve (WRSV)

A type of safety valve in which the principal components can be run and retrieved by wireline or slickline. The valve assembly is landed in a ported nipple that is equipped with a control line connected to the surface control system.

casing valve

A valve installed in the wellhead assembly to provide access to the casingannulus of non-producing casings.

depleted zone

An isolated section of reservoir in which the pressure has dropped below that of adjacent zones or the main body of the reservoir formation.

openhole gravel pack

A type of sand-control completion in which the gravel pack screen is packed off in an openhole section with no casing or liner to support the producing formation. The openhole interval is often prepared by underreaming a section of reservoir below the last casing shoe. When the treatment is to be applied on an existing well, a section of casing may be milled out.

wire wrapped screen

A type of screen used in sand control applications to support the gravel pack. The profiled wire is wrapped and welded in place on a perforated liner. Screens are available in a range of sizes and specifications, including outside diameter, material type and the geometry and dimension of the screen slots. The space between each wire wrap must be small enough to retain the gravel placed behind the screen, yet minimize any restriction to production.

pipe ram

A type of sealing element in high-pressure split seal blowout preventers that is manufactured with a half-circle hole on the edge (to mate with another horizontally opposed half) sized to fit around drillpipe.

diagenetic porosity

A type of secondary porosity created during diagenesis, commonly through dissolution or dolomitization or both. Diagenesis usually destroys porosity, so diagenetic porosity is rare.

moldic porosity

A type of secondary porosity created through the dissolution of a preexisting constituent of a rock, such as a shell, rock fragment or grain. The pore space preserves the shape, or mold, of the dissolved material.

fracture porosity

A type of secondary porosity produced by the tectonic fracturing of rock. Fractures themselves typically do not have much volume, but by joining preexisting pores, they enhance permeability significantly. In exceedingly rare cases, nonreservoir rocks such as granite can become reservoir rocks if sufficient fracturing occurs.

montmorillonite

A type of smectite clay mineral that tends to swell when exposed to water. this forms through the alteration of silicate minerals in alkaline conditions in basic igneous rocks, such as volcanic ash that can accumulate in the oceans. Montmorillonite is a component of bentonite commonly used in drilling fluids.

Sulfide-stress cracking

A type of spontaneous brittle failure in steels and other high-strength alloys when they are in contact with moist hydrogen sulfide and other sulfidic environments.

sulfide stress cracking

A type of spontaneous brittle failure in steels and other high-strength alloys when they are in contact with moist hydrogen sulfide and other sulfidic environments. Tool joints, hardened parts of blowoutpreventers and valve trim are particularly susceptible. For this reason, along with toxicity risks of hydrogen sulfide gas, it is essential that water muds be kept entirely free of soluble sulfides and especially hydrogen sulfide at low pH.

wrench fault

A type of strike-slip fault in which the fault surface is vertical, and the fault blocks move sideways past each other. Given the geological complexity of some deformed rocks, including rocks that have experienced more than one episode of deformation, it can be difficult to distinguish a wrench fault from a strike-slip fault. Also, areas can be deformed more than once or experience ongoing structuring such that fault surfaces can be rotated from their original orientations.

fault trap

A type of structural hydrocarbon trap in which closure is controlled by the presence of at least one fault surface.

anticlinal trap

A type of structural hydrocarbon trap whose closure is controlled by the presence of an anticline.

structure map

A type of subsurface map whose contours represent the elevation of a particular formation, reservoir or geologic marker in space, such that folds, faults and other geologic structures are clearly displayed. Its appearance is similar to that of a topographic map, but a topographic map displays elevations of the Earth's surface and a structure map displays the elevation of a particular rock layer, generally beneath the surface.

tubing-retrievable safety valve (TRSV)

A type of subsurface safety valve that is run and retrieved as part of the production tubing string. The ' ' ' ' body is integral part of the completion that enables the internal components to be configured to provide near fullbore access through the valve. An external control line is secured to the running string for connection to a surface-control system.

karst

A type of topography formed in areas of widespread carbonate rocks through dissolution. Sink holes, caves and pock-marked surfaces are typical features of a karst topography.

external upset

A type of tubing connection in which the external diameter of the tubing joint is larger adjacent to the tubing connection to provide the necessary strength. The internal tubing surface is flush to enable good fluid-flow characteristics.

flush joint

A type of tubing connection in which the internal or external surfaces are the same diameter throughout the tubing joint. Internal '' ''' are most common, offering no restriction to fluid flow. Externally ''' '''' are typically used in more specialized applications, such as washover pipe for fishingoperations, to allow adequate outer diameter (OD) clearance.

gate valve

A type of valve that incorporates a sliding gate to block fluid flow. The design of the valve operating and sealing systems typically requires that gate valves should be operated either fully open or fully closed.

orifice valve

A type of valve, typically found on small-diameter pipework, that incorporates an orifice or flow-restriction device to control fluid flow.

vitrinite

A type of woody kerogen that is relatively uniform in composition. Since vitrinite changes predictably and consistently upon heating, its reflectance is a useful measurement of source rock maturity. Strictly speaking, the plant material that forms vitrinite did not occur prior to Ordovician time. Also, because vitrinite originated in wood, its occurrence in marine rocks might be limited by the depositional processes that act in a given depositional environment.

Mils per year penetration

A unit of measurement for the corrosion rate of a coupon, abbreviated as mpy.

wing valve

A valve located on the side of a Christmas tree or temporary surface flow equipment, such as may be used for a drillstem test. Two are generally fitted to a Christmas tree. A flowing '' '' is used to control and isolate production, and the kill wing valve fitted on the opposite side of the Christmas tree is available for treatment or well-control purposes. The term typically is used when referring to the flowing wing.

gas lift valve

A valve used in a gas-lift system to control the flow of lift gas into the production tubing conduit. The '' '' '' is located in the gas-lift mandrel, which also provides communication with the lift gas supply in the tubing annulus. Operation of the '' '' '' is determined by preset opening and closing pressures in the tubing or annulus, depending on the specific application.

adjustable choke

A valve usually used in well control operations to reduce the pressure of a fluid from high pressure in the closed wellbore to atmospheric pressure. It may be adjusted (opened or closed) to closely control the pressure drop.

mist drilling

A variation of air drilling in which a small amount of water trickles into the wellbore from exposed formations and is carried out of the wellbore by the compressed air used for air drilling. The onset of this method of drilling often signals the impending end of practical air drilling, at which point the water inflow becomes too great for the compressed air to remove from the wellbore, or the produced water (usually salty) becomes a disposal problem.

stratigraphic trap

A variety of sealed geologic container capable of retaining hydrocarbons, formed by changes in rock type or pinch-outs, unconformities, or sedimentary features such as reefs. Structural traps, in contrast, consist of geologic structures in deformed strata such as faults and folds whose geometries permit retention of hydrocarbons.

structural trap

A variety of sealed geologic structure capable of retaining hydrocarbons, such as a fault or a fold. Stratigraphic traps form where changes in rock type can retain hydrocarbons.

spacer

A viscous fluid used to aid removal of drilling fluids before a primary cementing operation. prepared with specific fluid characteristics, such as viscosity and density, that are engineered to displace the drilling fluid while enabling placement of a complete cement sheath.

Preflush

A volume of brine whose purpose is to change (usually lower) the salinity of the resident brine, so that mixing with the surfactant will not cause loss of interfacial activity.

clear brine

A water-based solution of inorganic salts used as a well-control fluid during the completion andworkover phases of well operations.

brine

A water-based solution of inorganic salts used as a well-control fluid during the completion andworkover phases of well operations. '' are solids free, containing no particles that might plug or damage a producing formation. In addition, the salts in '' can inhibit undesirable formation reactions such as clay swelling. Brines are typically formulated and prepared for specific conditions, with a range of salts available to achieve densities ranging from 8.4 to over 20 lbm/gal (ppg) [1.0 to 2.4 g/cmo].

fold

A wave-like geologic structure that forms when rocks deform by bending instead of breaking under compressional stress. Anticlines are arch-shaped folds in which rock layers are upwardly convex. The oldest rock layers form the core of the fold, and outward from the core progressively younger rocks occur. A syncline is the opposite type of fold, having downwardly convex layers with young rocks in the core. Folds typically occur in anticline-syncline pairs. The hinge is the point of maximum curvature in a fold. The limbs occur on either side of the fold hinge. The imaginary surface bisecting the limbs of the fold is called the axial surface. The axial surface is called the axial plane in cases where the fold is symmetrical and the lines containing the points of maximum curvature of the folded layers, or hinge lines, are coplanar. Concentric folding preserves the thickness of each bed as measured perpendicular to original bedding. Similar folds have the same wave shape, but bed thickness changes throughout each layer, with thicker hinges and thinner limbs.

safety joint

A weak spot in the drillstring. Such a weak spot sometimes is intentionally put into the drillstring so that if tension in the drillstring exceeds a predetermined amount, the safety joint will part and the rest of the drillstring will be salvageable.

openhole completion

A well completion that has no casing or liner set across the reservoir formation, allowing the produced fluids to flow directly into the wellbore. This type of completion suffers the major disadvantage that the sandface is unsupported and may collapse.

barefoot completion

A well completion that has no casing or liner set across the reservoirformation, allowing the produced fluids to flow directly into the wellbore. This type of completion suffers the major disadvantage that the sandface is unsupported and may collapse. Also, without any casing or liner installed, selective treatments or remedial work within the reservoir section are more difficult.

intelligent well

A well equipped with monitoring equipment and completion components that can be adjusted to optimize production, either automatically or with some operator intervention.

Line drive

An injection pattern in which the injection wells are located in a straight line parallel to the production wells. The injected fluid, which is normally water, steam or gas, creates a nearly linear frontal movement.

injection well

A well in which fluids are injected rather than produced, the primary objective typically being to maintainreservoir pressure. Two main types of injection are common: gas and water. Separated gas fromproduction wells or possibly imported gas may be reinjected into the upper gas section of the reservoir. Water-injection wells are common offshore, where filtered and treated seawater is injected into a lower water-bearing section of the reservoir.

subsea well

A well in which the wellhead, Christmas tree and production-control equipment is located on the seabed.

gas well

A well that primarily produces natural gas.

marginal well

A well that, for reasons of depletion or natural low productivity, is nearing the limits of viable productionand profitability.

disposal well

A well, often a depleted oil or gas well, into which waste fluids can be injected for safe disposal. ''''' typically are subject to regulatory requirements to avoid the contamination of freshwater aquifers

rigless operation

A well-intervention operation conducted with equipment and support facilities that precludes the requirement for a rig over the wellbore. Coiled tubing, slickline and snubbing activities are commonly conducted as such

Fracture acidizing

A well-stimulation operation in which acid, usually hydrochloric [HCl], is injected into a carbonate formation at a pressure above the formation-fracturing pressure. Flowing acid tends to etch the fracture faces in a nonuniform pattern, forming conductive channels that remain open without a propping agent after the fracture closes.

cased hole

A wellbore lined with a string of casing or liner. Although the term can apply to any hole section, it is often used to describe techniques and practices applied after a casing or liner has been set across thereservoir zone, such as cased-hole logging or cased-hole testing.

bridge

A wellbore obstruction caused by a buildup of material such as scale, wellbore fill or cuttings that can restrict wellbore access or, in severe cases, eventually close the wellbore.

dry hole

A wellbore that has not encountered hydrocarbons in economically producible quantities

gauge hole

A wellbore that is essentially the same diameter as the bit that was used to drill it. It is common to find well-consolidated sandstones and carbonaterocks that remain so after being drilled. For clays, it is common for the hole to slowly enlarge with the passing of time, especially if water-base muds are being used.

deviated hole

A wellbore that is not vertical. The term usually indicates a wellbore intentionally drilled away from vertical.

directional well

A wellbore that requires the use of special tools or techniques to ensure that the wellbore path hits a particular subsurface target, typically located away from (as opposed to directly under) the surface location of the well.

production tubing

A wellbore tubular used to produce reservoir fluids.

casing bowl

A wellhead component or a profile formed in wellhead equipment in which thecasing hanger is located when a casing string has been installed. The ''' incorporates features to secure and seal the upper end of the casing string and frequently provides a port to enable communication with theannulus.

tubing head

A wellhead component that supports the tubing hanger and provides a means of attaching the Christmas tree to the wellhead.

casing spool

A wellhead component used in flanged wellhead assemblies to secure the upper end of a casing string.''' or bowls are available in a wide range of sizes and pressure ratings and are selected to suit the specific conditions.

swamp

A wetland depositional environment in which water is present either permanently or intermittently and in which trees and large woody plants can grow but peat does not form. Swamps can contain considerable quantities of organic matter.

dolomite

A widely-distributed carbonate mineral and chief constituent of dolostone. The name given to dolomitized limestone.

selective running tool

A wireline tool to set and retrieve selectively set downhole equipment such as plugs and similar flow-control devices. enables equipment to be set in a target nipple that may be one of a series placed throughout the wellbore.

tour

A work shift of a drilling crew.

seismite

An injectite attributable to earthquake or seismic shaking.

glacial

Pertaining to the environment of deposition by glaciers.

Universal Transverse Mercator grid (UTM)

A worldwide grid system of rectangular map coordinates that uses metric (SI) units. A location is specified on the basis of its location within one of 60 zones worldwide of 6o of longitude and 8o of latitude each that are subdivided into subzones that are 100,000 m [330,000 ft] on each side. Locations consist of a series of numbers and letters that can be accurate to within an area of one square meter. The headquarters of the Geological Society of America are at 13TDQ8743172 (Merrill, 1986). Information about the UTM grid, including grid ticks on quadrangle maps, can be found on most maps produced by the US Geological Survey. Latitude and longitude coordinates, or geographic coordinates, are another means of locating a point at the Earth's surface, but the accuracy, computer compatibility and uniqueness of UTM have resulted in its finding acceptance within the scientific community.

Wadati-Benioff zone

A zone of the upper mantle in which earthquakes occur when a lithospheric plate is subducted, named in honor of seismologists Kiyoo Wadati and Hugo Benioff. The dip of the Wadati-Benioff zone coincides with the dip of the subducting plate. The Wadati-Benioff zone extends to a depth of about 700 km [435 miles] from the Earth's surface.

Benioff zone

A zone of the upper mantle in which earthquakes occur when a lithospheric plate is subducted, named in honor of seismologists Kiyoo Wadati and Hugo Benioff. The dip of this zone, also referred to as the Wadati-Benioff zone, coincides with the dip of the subducting plate. The Wadati-Benioff zone extends to a depth of about 700 km [435 miles] from the Earth's surface.

CSG

Abbreviation for coal seam gas. Natural gas, predominantly methane [CH4], generated during coal formation and adsorbed in coal. Natural gas adsorbs to the surfaces of matrix pores within the coal and natural fractures, or cleats, as reservoir pressure increases.

CBM

Abbreviation for coalbed methane. Natural gas, predominantly methane [CH4], generated during coal formation and adsorbed in coal. Natural gas adsorbs to the surfaces of matrix pores within the coal and natural fractures, or cleats, as reservoir pressure increases.

elasticity

Ability of a material to undergo stress, deform, and then recover and return to its original shape after the stress ceases. Once stress exceeds the yield stress or elastic limit of a material, permanent deformation occurs and the material will not return to its original shape when the stress is removed. In some materials, including rocks, elastic behavior depends on the temperature and the duration of the stress as well as its intensity.

iron stabilizer

Also known as a chelating agent, a chemical added to an acid to stabilize iron. In the oil field, acid is used in stimulation treatments and to treat or remove scale or weighting material in reservoir drilling fluids.The injected acid dissolves iron from rust, millscale, iron scales or iron-containing minerals in the formation. Iron can exist as ferric iron [Fe+3] or ferrous iron [Fe+2]. If the iron is not controlled, it will precipitate insoluble products such as ferric hydroxide and, in sour environments, ferrous sulfide [FeS], which will damage the formation.

well sticking

Also known as differential sticking, a condition whereby the drillstringcannot be moved (rotated or reciprocated) along the axis of the wellbore.

temperature gradient

Also known as geothermal gradient, the rate of increase in temperature per unit depth in the Earth. Although the geothermal gradient varies from place to place, it averages 25 to 30 °C/km [15 °F/1000 ft]. Temperature gradients sometimes increase dramatically around volcanic areas. It is particularly important for drilling fluids engineers to know the geothermal gradient in an area when they are designing a deep well. The downhole temperature can be calculated by adding the surface temperature to the product of the depth and the geothermal gradient.

thermal gradient

Also known as geothermal gradient, the rate of increase in temperature per unit depth in the Earth. Although the geothermal gradient varies from place to place, it averages 25 to 30 °C/km [15 °F/1000 ft]. Temperature gradients sometimes increase dramatically around volcanic areas. It is particularly important for drilling fluids engineers to know the geothermal gradient in an area when they are designing a deep well. The downhole temperature can be calculated by adding the surface temperature to the product of the depth and the geothermal gradient.

formation evaluation while drilling

Also known as logging while drilling or LWD, the measurement of formation properties during the excavation of the hole, or shortly thereafter, through the use of tools integrated into the bottomhole assembly.

tectonics

Also known as plate tectonics, the unifying geologic theory developed to explain observations that interactions of the brittle plates of the lithosphere with each other and with the softer underlying asthenosphere result in large-scale changes in the Earth. The theory of plate tectonics initially stemmed from observations of the shapes of the continents, particularly South America and Africa, which fit together like pieces in a jigsaw puzzle and have similar rocks and fossils despite being separated by a modern ocean. As lithospheric plates heat up or cool down depending on their position, or their tectonic environment, relative to each other and to warmer areas deeper within the Earth, they become relatively more or less dense than the asthenosphere and thus tend to rise as molten magma or sink in cold, brittle slabs or slide past each other. Mountain belts can form during plate collisions or an orogeny; diverging plates or rifts can create new midoceanic ridges; plates that slide past one another create transform fault zones (such as the San Andreas fault); and zones of subduction occur where one lithospheric plate moves beneath another. Plate tectonic theory can explain such phenomena as earthquakes, volcanic or other igneous activity, midoceanic ridges and the relative youth of the oceanic crust, and the formation of sedimentary basins on the basis of their relationships to lithospheric plate boundaries. Convection of the mantle is postulated to be the driving mechanism for the movement of lithospheric plates. Measurements of the continents using the Global Positioning System confirm the relative motions of plates. Age determinations of the oceanic crust confirm that such crust is much younger than that of the continents and has been recycled by the process of subduction and regenerated at midoceanic ridges.

travel joint

Also known as slip joint, a completion component designed to accommodate tubing movement or length changes while maintaining a hydraulic seal between the production conduit and the annulus. The size or length of the slip joint depends on the wellbore conditions and completion characteristics.

travel joint

Also known as slip joint, a telescoping joint at the surface in floating offshore operations that permits vessel heave (vertical motion) while maintaining a riser pipe to the seafloor. As the vessel heaves, the slip joint telescopes in or out by the same amount so that the riser below the slip joint is relatively unaffected by vessel motion.

low velocity layer

Also known as weathered layer, a near-surface, possibly unconsolidated layer of low seismic velocity. The base of the weathered layer commonly coincides with the water table and a sharp increase in seismic velocity. The weathered layer typically has air-filled pores.

formation damage

Alteration of the far-field or virgin characteristics of a producing formation, usually by exposure to drilling fluids. The water or solid particles in the drilling fluids, or both, tend to decrease the pore volume and effective permeability of the producible formation in the near-wellbore region.

wiper trip

An abbreviated recovery and replacement of the drillstring in the wellbore that usually includes the bit and bottomhole assembly passing by all of the openhole, or at least all of the openhole that is thought to be potentially troublesome.

short trip

An abbreviated recovery of pipe out of, and then the replacement of same back into the wellbore. The recovery of pipe out of the wellbore is normally limited to 10 or 20 stands of drillpipe.

quartz

An abundant rock-forming mineral composed of silicon and oxygen, also called silica. Quartz sand grains are a major constituent of sandstone and other clastic sedimentary rocks.

oil field

An accumulation, pool or group of pools of oil in the subsurface. A this consists of a reservoir in a shape that will trap hydrocarbons and that is covered by an impermeable or sealing rock. Typically, industry professionals use the term with an implied assumption of economic size.

field

An accumulation, pool, or group of pools of hydrocarbons or other mineral resources in the subsurface. A hydrocarbon field consists of a reservoir in a shape that will trap hydrocarbons and that is covered by an impermeable, sealing rock. Typically, the term implies an economic size.

drift

An accurately machined device that is pulled through the casing, tubulars and completion components to ensure minimum-diameter specifications are within tolerance, as described in definition 2. While this tool is usually of a short length, the well planner may specify a special drift that either has a longer length or a nonstandard outside diameter. The large-diameter casing drifts are frequently known as "rabbits."

perforating acid

An acid treatment placed in the wellbore over the interval to be perforated. Because of the overbalanceconditions at the time of perforating, the ''' ''' is forced into the newly formed perforationtunnel to stimulate the crushed zone

Hydrochloric acid

An acid type commonly used in oil- and gas- well stimulation, especially in carbonate formations.

kelly bushing (KB) OR rotary bushing

An adapter that serves to connect the rotary table to the kelly. It has an inside diameter profile that matches that of the kelly, usually square or hexagonal. It is connected to the rotary table by four large steel pins that fit into mating holes in the rotary table. The rotary motion from the rotary table is transmitted to this adapter through the pins, and then to the kelly itself through the square or hexagonal flat surfaces between the this adapter and the kelly. The kelly then turns the entire drillstring because it is screwed into the top of the drillstring itself.

plunger lift

An artificial-lift method principally used in gas wells to unload relatively small volumes of liquid. An automated system mounted on the wellhead controls the well on an intermittent flow regime. When the well is shut-in, a plunger is dropped down the production string. When the control system opens the well for production, the plunger and a column of fluid are carried up the tubing string. The surface receiving mechanism detects the plunger when it arrives at surface and, through the control system, prepares for the next cycle.

intermittent gas lift

An artificial-lift method, used in relatively low-productivity wells, in which the gas-lift system is operated on an intermittent basis to enable the buildup of liquids in the wellbore.

rock

An aggregate of minerals or organic matter (in the case of coal, which is not composed of minerals because of its organic origin), or volcanic glass (obsidian, which forms a rock but is not considered a mineral because of its amorphous, noncrystalline nature). Rocks can contain a single mineral, such as rock salt (halite) and certain limestones (calcite), or many minerals, such as granite (quartz, feldspar, mica and other minerals). There are three main types of rocks. Sedimentary rocks like sandstone and limestone form at the Earth's surface through deposition of sediments derived from weathered rocks, biogenic activity or precipitation from solution. Igneous rocks originate deeper within the Earth, where the temperature is high enough to melt rocks, to form magma that can crystallize within the Earth or at the surface by volcanic activity. Metamorphic rocks form from other preexisting rocks during episodes of deformation of the Earth at temperatures and pressures high enough to alter minerals but inadequate to melt them. Such changes can occur by the activity of fluids in the Earth and movement of igneous bodies or regional tectonic activity. Rocks are recycled from one type to another by the constant changes in the Earth.

pressure buildup analysis

An analysis of data obtained from measurements of the bottomhole pressure in a well that is shut-in after a flow period. The profile created on a plot of pressure against time is used with mathematical reservoirmodels to assess the extent and characteristics of the reservoir and the near-wellbore area.

stratigraphic analysis

An analysis of the history, composition, relative ages and distribution of strata, and the interpretation of strata to elucidate Earth history. The comparison, or correlation, of separated strata can include study of their lithology, fossil content, and relative or absolute age, or lithostratigraphy, biostratigraphy, and chronostratigraphy.

NODAL* analysis

An analytical tool used in forecasting the performance of the various elements comprising thecompletion and production system.'' ''' is used to optimize the completion design to suit the reservoir deliverability, identify restrictions or limits present in the production system and identify any means of improving production efficiency.

anticline

An arch-shaped fold in rock in which rock layers are upwardly convex. The oldest rock layers form the core of the fold, and outward from the core progressively younger rocks occur. Anticlines form many excellent hydrocarbon traps, particularly in folds with reservoir-quality rocks in their core and impermeable seals in the outer layers of the fold. A syncline is the opposite type of fold, having downwardly convex layers with young rocks in the core.

point bar

An arcuate deposit of sediment, usually sand, that occurs along the convex inner edges of the meanders of channels and builds outward as the stream channel migrates.

play

An area in which hydrocarbon accumulations or prospects of a given type occur. For example the shale gas plays in North America include the Barnett, Eagle Ford, Fayetteville, Haynesville, Marcellus, and Woodford, among many others. Outside North America, shale gas potential is being pursued in many parts of Europe, Africa, Asia, and South America.

delta

An area of deposition or the deposit formed by a flowing sediment-laden current as it enters an open or standing body of water, such as a river spilling into a gulf. As a river enters a body of water, its velocity drops and its ability to carry sediment diminishes, leading to deposition. The term has origins in Greek because the shape of deltas in map view can be similar to the Greek letter delta. The shapes of deltas are subsequently modified by rivers, tides and waves. There is a characteristic coarsening upward of sediments in a delta. The three main classes of deltas are river-dominated (Mississippi River), wave-dominated (Nile River), and tide-dominated (Ganges River). Ancient deltas contain some of the largest and most productive petroleum systems.

prospect

An area of exploration in which hydrocarbons have been predicted to exist in economic quantity. This is commonly an anomaly, such as a geologic structure or a seismic amplitude anomaly, that is recommended by explorationists for drilling a well. Justification for drilling a prospect is made by assembling evidence for an active petroleum system, or reasonable probability of encountering reservoir-quality rock, a trap of sufficient size, adequate sealing rock, and appropriate conditions for generation and migration of hydrocarbons to fill the trap. A single drilling location is also called a prospect, but the term is more properly used in the context of exploration. A group of prospects of a similar nature constitutes a play.

hydrocarbon kitchen

An area of the subsurface where source rock has reached appropriate conditions of pressure and temperature to generate hydrocarbons; also known as source kitchen, oil kitchen or gas kitchen.

oil kitchen

An area of the subsurface where source rock has reached appropriate conditions of pressure and temperature to generate liquid hydrocarbons as opposed to gas.

manifold

An arrangement of piping or valves designed to control, distribute and often monitor fluid flow.

continuous gas lift

An artificial-lift method in which the gas-lift system is operated on a continuous basis to sustain liquidproduction at an efficient rate.

beam pump

An artificial-lift pumping system using a surface power source to drive a downhole pump assembly. A beam and crank assembly creates reciprocating motion in a sucker-rod string that connects to the downhole pump assembly. The pump contains a plunger and valve assembly to convert the reciprocating motion to vertical fluid movement.

sucker rod pump

An artificial-lift pumping system using a surface power source to drive a downhole pump assembly. A beam and crank assembly creates reciprocating motion in a sucker-rod string that connects to the downhole pump assembly. The pump contains a plunger and valve assembly to convert the reciprocating motion to vertical fluid movement.

electric submersible pump

An artificial-lift system that utilizes a downhole pumping system that is electrically driven. The pump typically comprises several staged centrifugal pump sections that can be specifically configured to suit the production and wellbore characteristics of a given application. ' '''' '' systems are a common artificial-lift method, providing flexibility over a range of sizes and output flow capacities.

casing string

An assembled length of steel pipe configured to suit a specific wellbore. The sections of pipe are connected and lowered into a wellbore, then cemented in place.

casing string

An assembled length of steel pipe configured to suit a specific wellbore. The sections of pipe are connected and lowered into a wellbore, then cemented in place. The pipe joints are typically approximately 40 ft [12 m] in length, male threaded on each end and connected with short lengths of double-female threaded pipe called couplings. To protect or isolate formations adjacent to the wellbore.

Christmas tree

An assembly of valves, spools, pressure gauges and chokes fitted to thewellhead of a completed well to control production. Christmas trees are available in a wide range of sizes and configurations, such as low- or high-pressure capacity and single- or multiple-completion capacity.

electrodynamic brake

An electric motor that acts as a brake. Braking is accomplished by reversing the electric fields on the motor, effectively turning it into a generator. The usage of the generated power, either in useful applications or dissipation as heat, restrains the motor-turned-generator and provides a braking action.

Cable Head

An electromechanical device used to connect an electrical tool string to a logging cable, electrical wireline or coiled tubing string equipped with an electrical conductor. It provides attachments to both the mechanical armor wires and the outer mechanical housing of a logging tool, usually by means of threads.

cable head

An electromechanical device used to connect an electrical tool string to a logging cable, electricalwireline or coiled tubing string equipped with an electrical conductor. It provides attachments to both the mechanical armor wires (which give logging cable its tensile strength) and the outer mechanical housing of a logging tool, usually by means of threads.

Low-salinity waterflooding

An enhanced oil recovery method that uses water with a low concentration of dissolved salts as a flooding medium.

Surfactant flooding

An enhanced oil recovery process in which a small amount of surfactant is added to an aqueous fluid injected to sweep the reservoir.

Surfactant-alternating-gas

An enhanced oil recovery process in which alternating slugs of a surfactant solution and gas are injected into a reservoir. The injected surfactant and gas mix and generate foam that reduces the gas mobility, especially in previously swept or high-permeability regions of the reservoir.

High-pressure air injection

An enhanced oil recovery process utilizing compressed air that is injected into a reservoir. Oxygen in the gas reacts exothermically with some of the oil, producing highly mobile flue gas. The flue gas advances ahead of the reaction front and achieves an efficient displacement of the in situ oil.

Micellar polymer flooding

An enhanced oil recovery technique in which a micelle solution is pumped into a reservoir through specially distributed injection wells. The chemical solution reduces the interfacial and capillary forces between oil and water and triggers an increase in oil production.

Polymer flooding

An enhanced oil recovery technique using water viscosified with soluble polymers. Viscosity is increased until the mobility of the injectant is less than that of the oil phase in place, so the mobility ratio is less than unity. This condition maximizes oil-recovery sweep efficiency, creating a smooth flood front without viscous fingering.

horizon

An informal term used to denote a surface in or of rock, or a distinctive layer of rock that might be represented by a reflection in seismic data. The term is often used incorrectly to describe a zone from which hydrocarbons are produced.

Microbial enhanced oil recovery

An enhanced recovery process in which microorganisms are used in a reservoir to improve oil recovery. The microorganism can either be injected into the reservoir, or the population of an existing microorganism in the reservoir can be enhanced by injection of nutrients preferred by that microorganism. The microorganisms improve oil recovery by various means: (1) by releasing gases and increasing the pressure of the reservoir; (2) by breaking the heavier molecules into smaller chain components, resulting in the reduction of viscosity of oil; and 3) by producing natural surfactants that can improve oil flow by altering the interfacial properties of the system comprising the crude oil, brine and rock.

sabkha

An environment of coastal sedimentation characterized by arid or semiarid conditions above the level of high tide and by the absence of vegetation. Evaporites, eolian deposits and tidal-flood deposits are common in sabkhas.

dope

An especially formulated blend of lubricating grease and fine metallic particles that prevents thread galling (a particular form of metal-to-metal damage) and seals the roots or void spaces of threads.

offset well OR offset

An existing wellbore close to a proposed well that provides information for planning the proposed well.

Offset Well

An existing wellbore close to a proposed well that provides information for planning the proposed well. In planning development wells, there are usually numerous of this type of well, so a great deal is known about the subsurface geology and pressure regimes

Oil swelling

An expansion in oil volume that can occur when a solvent contacts a reservoir fluid.

subsalt

An exploration and production play type in which prospects exist below salt layers. Until relatively recently, many explorationists did not seek prospects below salt because seismic data had been of poor quality below salt (i.e., it was not possible to map traps accurately) or because they believed that reservoir-quality rock or hydrocarbons did not exist below salt layers. Advances in seismic processing and compelling drilling results from exploration wells encouraged companies to generate and drill prospects below salt layers, salt sheets and other previously disregarded potential traps. The offshore Gulf of Mexico contains numerous subsalt-producing fields, and similar areas are being explored internationally.

wildcat

An exploration well. The significance of this type of well to the drilling crew and well planners is that by definition, little if anything about the subsurface geology is known with certainty, especially the pressure regime.

hydrogen sulphide

An extraordinarily poisonous gas with a molecular formula of H2S. At low concentrations, H2S has the odor of rotten eggs, but at higher, lethal concentrations, it is odorless. H2S is hazardous to workers and a few seconds of exposure at relatively low concentrations can be lethal, but exposure to lower concentrations can also be harmful.

hydrogen sulfide

An extraordinarily poisonous gas with a molecular formula of H2S. At low concentrations, H2S has the odor of rotten eggs, but at higher, lethal concentrations, it is odorless. H2S is hazardous to workers and a few seconds of exposure at relatively low concentrations can be lethal, but exposure to lower concentrations can also be harmful. The effect of H2S depends on duration, frequency and intensity of exposure as well as the susceptibility of the individual.

Wet combustion

An in situ combustion technique in which water is injected simultaneously or alternately with air into a formation.

Toe to heel air injection - THAI

An in-situ combustion method for producing heavy oil. In this technique, the fireflooding starts from a vertical well, while the oil is produced from a horizontal well having its toe in close proximity to the vertical air-injection well.

Directional Driller

An individual trained in the science and art of intentionally drilling a well along a predetermined path in three-dimensional space, usually involving deviating the well from vertical and directing it in a specific compass direction or heading.

directional driller (DD)

An individual trained in the science and art of intentionally drilling a well along a predetermined path in three-dimensional space, usually involving deviating the well from vertical and directing it in a specific compass direction or heading.

turbidity current

An influx of rapidly moving, sediment-laden water down a slope into a larger body of water; also called a density current because the suspended sediment results in the current having a higher density than the clearer water into which it flows. Such currents can occur in lakes and oceans, in some cases as by-products of earthquakes or mass movements such as slumps. The sedimentary deposits that form as the current loses energy are called turbidites and can be preserved as Bouma sequences. Turbidity currents are characteristic of trench slopes of convergent plate margins and continental slopes of passive margins.

density current

An influx of rapidly moving, sediment-laden water down a slope into a larger body of water; the suspended sediment causes the current to have a higher density than the clearer water into which it flows, hence the name. Such currents can occur in lakes and oceans, in some cases as by-products of earthquakes or mass movements such as slumps. The sedimentary deposits that form as the current loses energy are called turbidites and can be preserved as Bouma sequences. Density currents are characteristic of trench slopes of convergent plate margins and continental slopes of passive margins.

swellable packer

An isolation device that relies on elastomers to expand and form an annular seal when immersed in certain wellbore fluids. The elastomers used in these packers are either oil- or water-sensitive.

swellable packer

An isolation device that relies on elastomers to expand and form an annular seal when immersed in certain wellbore fluids. The elastomers used in these packers are either oil- or water-sensitive. Their expansion rates and pressure ratings are affected by a variety of factors. Oil-activated elastomers, which work on the principle of absorption and dissolution, are affected by fluid temperature as well as the concentration and specific gravity of hydrocarbons in a fluid. Water-activated elastomers are typically affected by water temperature and salinity. This type of elastomer works on the principle of osmosis, which allows movement of water particles across a semi-permeable membrane based on salinity differences in the water on either side of the membrane.

cement retainer

An isolation tool set in the casing or liner that enables treatments to be applied to a lower interval while providing isolation from the annulus above. ''' are typically used in cement squeeze or similar remedial treatments. A specially profiled probe, known as a stinger, is attached to the bottom of the tubing string to engage in the retainer during operation. When the stinger is removed, the valve assembly isolates the wellbore below the cement retainer.

Micelle

An ordered aggregate of surfactant molecules formed when the surfactant concentration in a solution reaches a critical point, thus lowering the free energy of the system.

unconventional resource

An umbrella term for oil and natural gas that is produced by means that do not meet the criteria for conventional production. What has qualified as unconventional at any particular time is a complex function of resource characteristics, the available exploration and production technologies, the economic environment, and the scale, frequency and duration of production from the resource. Perceptions of these factors inevitably change over time and often differ among users of the term. At present, the term is used in reference to oil and gas resources whose porosity, permeability, fluid trapping mechanism, or other characteristics differ from conventional sandstone and carbonate reservoirs. Coalbed methane, gas hydrates, shale gas, fractured reservoirs, and tight gas sands are considered unconventional resources.

methane hydrate

An unusual occurrence of hydrocarbon in which molecules of methane are trapped in ice molecules. More generally, hydrates are compounds in which gas molecules are trapped within a crystal structure. Hydrates form in cold climates, such as permafrost zones and in deep water. To date, economic liberation of hydrocarbon gases from hydrates has not occurred, but hydrates contain quantities of hydrocarbons that could be of great economic significance. Hydrates can affect seismic data by creating a reflection or multiple.

clathrate

An unusual occurrence of hydrocarbon in which molecules of natural gas, typically methane, are trapped in ice molecules. More generally, hydrates are compounds in which gas molecules are trapped within a crystal structure. Hydrates form in cold climates, such as permafrost zones and in deep water. To date, economic liberation of hydrocarbon gases from hydrates has not occurred, but hydrates contain quantities of hydrocarbons that could be of great economic significance. Hydrates can affect seismic data by creating a reflection or multiple.

gas hydrate

An unusual occurrence of hydrocarbon in which molecules of natural gas, typically methane, are trapped in ice molecules. More generally, hydrates are compounds in which gas molecules are trapped within a crystal structure. Hydrates form in cold climates, such as permafrost zones and in deep water. To date, economic liberation of hydrocarbon gases from hydrates has not occurred, but hydrates contain quantities of hydrocarbons that could be of great economic significance. Hydrates can affect seismic data by creating a reflection or multiple.

hydrate

An unusual occurrence of hydrocarbon in which molecules of natural gas, typically methane, are trapped in ice molecules. More generally, hydrates are compounds in which gas molecules are trapped within a crystal structure. Hydrates form in cold climates, such as permafrost zones and in deep water. To date, economic liberation of hydrocarbon gases from hydrates has not occurred, but hydrates contain quantities of hydrocarbons that could be of great economic significance. Hydrates can affect seismic data by creating a reflection or multiple.

Wentworth scale

Another name for the Udden-Wentworth scale, a grade scale for classifying the diameters of sediments. Particles larger than 64 mm in diameter are classified as cobbles. Smaller particles are pebbles, granules, sand and silt. Those smaller than 0.0039 mm are clay. Several other grain size scales are in use, but the Udden-Wentworth scale (commonly called the Wentworth scale) is the one that is most frequently used in geology.

combination string

Another term for a tapered string: a string of drillpipe or casing that consists of two or more sizes or weights.

frac balls

Another term for ball sealers, small spheres designed to seal perforations that are accepting the most fluid, thereby diverting reservoir treatments to other portions of the target zone. Ball sealers are incorporated into the treatment fluid and pumped with it. The effectiveness of this type of mechanical diversion to keep the balls in place is strongly dependent on the differential pressure across theperforation and the geometry of the perforation itself.

wiper plug

Another term for cementing plug, a rubber plug used to separate the cement slurry from other fluids, reducing contamination and maintaining predictable slurry performance.

sequestering agent

Another term for chelating agent, a chemical used to bind metal ions to form a ring structure. Chelating agents stabilize or prevent the precipitation of damaging compounds. In the oil field, chelating agents are used in stimulation treatments and for cleaning surface facilities. They are also used to treat or remove scale or weighting agents in reservoir drilling fluids.

endless tubing

Another term for coiled tubing, a long, continuous length of pipe wound on a spool.

rotary bushing

Another term for kelly bushing, an adapter that serves to connect the rotary table to the kelly. The kelly bushing has an inside diameter profile that matches that of the kelly, usually square or hexagonal.

lock mandrel

Another term for lock, a downhole device, run and retrieved on slickline, that is placed and anchored within the tubing string to provide a setting point for flow-control equipment such as valves, chokes and plugs.

nitrogen kickoff

Another term for nitrogen lift, the use of nitrogen gas circulated into the production conduit to displace liquids and reduce the hydrostatic pressure created by the fluid column. Nitrogen lifting is a common technique used to initiate production on a well following workover or overbalanced completion. A coiled tubing string is generally used to apply the treatment, which involves running to depth while pumping high-pressure nitrogen gas. Once the kill-fluid column is unloaded and the well is capable of natural flow, the coiled tubing string is removed and the well is prepared for production.

safety joint

Another term for release joint, a downhole tool that is designed to part under controlled conditions. A release joint enables part of the tool string to be left in the wellbore while the running string is retrieved.

setting tool

Another term for running tool, a generic name for a tool or device that is used in the placement or setting of downhole equipment such as permanent packers or plugs. The running tool can be retrieved after the operation or setting process. In some cases, the running tool also is used to retrieve the equipment or tool that has been set in the wellbore.

crooked hole

Antiquated term for a deviated wellbore, usually used to describe a well deviated accidentally during the drilling process.

formation fluid

Any fluid that occurs in the pores of a rock. Strata containing different fluids, such as various saturations of oil, gas and water, may be encountered in the process of drilling an oil or gas well. Fluids found in the target reservoir formation are referred to as '' '''

lag gas

Any gas deliberately introduced into the mud system to help a mudlogger or wellsite geologist track the amount of time or the number of mud pump strokes it takes to circulate mud from the kelly downhole through the drillstring to the bit, and back uphole to the gas trap at the shale shaker. This interval is used to calculate the lag period.

spacer fluid

Any liquid used to physically separate one special-purpose liquid from another. Special-purpose liquids are typically prone to contamination, so the liquid used must be compatible with both.

injection pump

Any pump used to inject fluid into the reservoir or production system. These pumps vary in volume andpressure capacity, from the large pumps used in water-injection wells, to much smaller low-volume pumps used in continuous scale-inhibitor treatments.

pill

Any relatively small quantity (less than 200 bbl) of a special blend of drilling fluid to accomplish a specific task that the regular drilling fluid cannot perform. Examples include high-viscosity pills to help lift cuttings out of a vertical wellbore, freshwater pills to dissolve encroaching salt formations, pipe-freeing pills to destroy filter cake and relieve differential sticking forces and lost circulation material pills to plug a thief zone.

nipple

Any short piece of pipe, especially if threaded at both ends with male threads.

sub

Any small component of the drillstring, such as a short drill collar or a thread crossover. Also a slang for substructure, which is the part of the rig that supports the derrick, rig floor and associated equipment.

liner

Any string of casing in which the top does not extend to the surface but instead is suspended from inside the previous casing string. Many conventional well designs include a production liner set across the reservoir interval.

artificial lift

Any system that adds energy to the fluid column in a wellbore with the objective of initiating and improving production from the well. These systems use a range of operating principles, including rod pumping, gas lift and electric submersible pump

connection

Any threaded or nonthreaded union or joint that connects two tubular components. The act of adding a joint or stand of drillpipe to the top of the drillstring,

connection

Any threaded or nonthreaded union or joint that connects two tubular components. The act of adding a joint or stand of drillpipe to the top of the drillstring, also described as "making a connection."

roustabout

Any unskilled manual laborer on the rigsite. This laborer may be part of the drilling contractor's employee workforce, or may be on location temporarily for special operations

Aquifer

Any water-bearing formation encountered while drilling.

junk

Anything in the wellbore that is not supposed to be there. The term is usually reserved for small pieces of steel such as hand tools, small parts,bit nozzles, pieces of bits or other downhole tools, and remnants of millingoperations.

vesicle

Bubble-shaped cavities in volcanic rock formed by expansion of gas dissolved in the precursor magma.

3)The hot water that condenses from the steam and the steam itself generate an artificial drive that sweeps oil toward producing wells.

By what mechanisms does a steam flood enhance oil recovery?

gas coning

Change in the gas-oil contact profile as a result of drawdown pressures during production. ''' occurs in vertical or slightly deviated wells and is affected by the characteristics of the fluids involved and the ratio of horizontal to vertical permeability.

cement additive

Chemicals and materials added to a cement slurry to modify the characteristics of the slurry or set cement. '' may be broadly categorized as accelerators, retarders, fluid-loss additives, dispersants, extenders, weighting agents, lost circulation additives and special additives designed for specific operating conditions. ''' are commonly available in powder or liquid form, enabling some flexibility in how the cement slurry is prepared.

hot oiling

Circulation of heated fluid, typically oil, to dissolve or dislodge paraffin deposits from the productiontubing. Such deposits tend to occur where a large variation in temperature exists across the producing system.

cherty

Containing chert, a sedimentary rock and a variety of quartz made of extremely fine-grained, or cryptocrystalline, silica, also called chalcedony. The silica might be of organic origin, such as from the internal structures of sponges called spicules, or inorganic origin, such as precipitation from solution. The latter results in the formation of flint. Chert can form beds, but is more common as nodules in carbonate rocks.

sour

Contaminated with sulfur or sulfur compounds, especially hydrogen sulfide. Crude oil and gas that are sour typically have an odor of rotten eggs if the concentration of sulfur is low. At high concentrations, sulfur is odorless and deadly.

The Gibbs free energy per unit area of interface at fixed temperature and pressure.

Define interfacial tension in terms of Gibbs free energy...

Oil that does not move when fluids are flowed through the rock in normal conditions, for example primary and secondary recovery, and invasion.

Define residual oil

The solubility of a substance is its concentration in a saturated solution.

Define solubility

Spontaneous imbibition refers to the process of absorption with no pressure driving the phase into the rock.

Define spontaneous imbibition

micrite

Dense, fine-grained carbonate mud or rocks composed of mud that forms by erosion of larger carbonate grains, organic precipitation (such as from algae), or inorganic precipitation. The grains in micrite are generally less than 4 microns in size.

2) Alters wettability of the reservoir rock

Describe two mechanisms by which surfactant flooding improves oil recovery.

competent

Describes a bed that maintains its original thickness during deformation. Often pertains to relatively brittle, solid strata that deform by faulting, fracturing or folding, rather than flowing under stress. Incompetent beds are more ductile and tend to flow under stress, so their bed thickness changes more readily during deformation.

ball-operated

Describing a mechanism or system that is actuated by a ball that is dropped or pumped through the tubing string. Once located on a landing seat, the tool mechanism is generally actuated by hydraulic pressure.

ball operated

Describing a mechanism or system that is actuated by a ball that is dropped or pumped through the tubing string. Once located on a landing seat, the tool mechanism is generally actuated by hydraulicpressure.

tight

Describing a relatively impermeable reservoir rock from which hydrocarbon production is difficult. Reservoirs can be tight because of smaller grains or matrix between larger grains, or they might be tight because they consist predominantly of silt- or clay-sized grains, as is the case for shale reservoirs. Stimulation of tight formations can result in increased production from formations that previously would have been abandoned or produced uneconomically.

palustrine

Describing material deposited in or growing in a marsh.

en echelon

Describing parallel or subparallel, closely-spaced, overlapping or step-like minor structural features in rock, such as faults and tension fractures, that are oblique to the overall structural trend.

argillaceous

Describing rocks or sediments containing particles that are silt- or clay-sized, less than 0.625 mm in size. Most have a high clay-mineral content, and many contain a sufficient percentage of organic material to be considered a source rock for hydrocarbon.

arenaceous

Describing sandy-textured rock or sediment. This does not necessarily imply silica-rich, but rather particles of sand size, 0.625 to 2 mm, according to the Udden-Wentworth scale.

dirty

Describing sedimentary rock that contains clay minerals. Even small amounts of clay minerals in pores can drastically reduce porosity and permeability. Dirty and clean are qualitative, descriptive terms to describe the relative amount of clay minerals in a rock.

isotropic

Directionally uniform, such that the physical properties of the material do not vary in different directions. In rocks, changes in physical properties in different directions, such as the alignment of mineral grains or the seismic velocity measured parallel or perpendicular to bedding surfaces, are forms of anisotropy. (Compare with homogeneity).

solution gas

Dissolved gas in wellbore or reservoir fluids. The gas will remain in solution until the pressure or temperature conditions change, at which time it may break out of solution to become free gas.

zip collars

Drill collars (usually straight drill collars) that have been machined with a reduced diameter at the box (up) end so that they may be more easily handled with open-and-close elevators.

gas cut mud

Drilling fluid whose bulk, unpressurized density is reduced as a small volume of gas displaces an equivalent volume of liquid.

deep-water play

Exploration activity located in offshore areas where water depths exceed approximately 600 feet [200 m], the approximate water depth at the edge of the continental shelf. While deep-water reservoir targets are geologically similar to reservoirs drilled both in shallower present-day water depths as well as onshore, the logistics of producing hydrocarbons from reservoirs located below such water depths presents a considerable technical challenge.

deepwater play

Exploration activity located in offshore areas where water depths exceed approximately 600 feet [200 m], the approximate water depth at the edge of the continental shelf. While deep-water reservoir targets are geologically similar to reservoirs drilled both in shallower present-day water depths as well as onshore, the logistics of producing hydrocarbons from reservoirs located below such water depths presents a considerable technical challenge.

flower structure

Folded structures associated with strike-slip faults. In areas where strike-slip faults occur in converging crust, or transpression, rocks are faulted upward in a positive flower structure. In areas of strike-slip faulting in diverging crust, or transtension, rocks drop down to form a negative flower structure. Flower structures can form hydrocarbon traps. The term "flower structure" reflects the resemblance of the structure to the petals of a flower in cross section.

dry gas

Gas produced from a well that produces little or no condensate or reservoir liquids. The production of liquids from gas wells complicates the design and operation of surface process facilities required to handle and export the produced gas.

contamination gas

Gas that is introduced into the drilling mud from a source other than the formation. It normally evolves as a by-product of oil-base mud systems and those using volatile additives such as diesel fuel or other lubricants.

contamination gas

Gas that is introduced into the drilling mud from a source other than the formation. This gas normally evolves as a by-product of oil-base mud systems and those using volatile additives such as diesel fuel or other lubricants.

gas show

Gas that rises to the surface, usually detected because it reduces the density of the drilling mud. Gas detectors, which the mud logger monitors, measure combustible gases (methane, ethane, butane and others). The mud logger reports total gas, individual gas components, or both, on the mud log. In extreme cases, gas visibly bubbles out of the mud as it returns to the surface.

rheology

Generally, the study of how matter deforms and flows, including its elasticity, plasticity and viscosity. In geology, rheology is particularly important in studies of moving ice, water, salt and magma, as well as in studies of deforming rocks.

Clays such as barite or kaolinite

Give an example of a hydophilic subtance

Gasdrive (gas cap or solution gasdrive), waterdrive (bottomwater drive or edgewater drive), combination drive, and gravity drainage

Give examples of reservoir drive mechanisms

4) Reducing heat transfer to maintain the oil temperature above its cloud point - for example by filling the annulus of the well with a fluid that has poor heat transfer properties

Give four examples of paraffin control measures.

b. Eliminates lost circulation problems

Give two advantages of Air Drilling

b. Destabilization of the borehole wall due to the absence of wellbore pressure (which is usually provided by liquids)

Give two disadvantages of Air Drilling

eustasy

Global sea level variations. Changes in sea level can result from movement of tectonic plates altering the volume of ocean basins, or when changes in climate affect the volume of water stored in glaciers and in polar icecaps. Eustasy affects positions of shorelines and processes of sedimentation, so interpretation of eustasy is an important aspect of sequence stratigraphy.

Preflush

In chemical flooding, a fluid stage, normally low-salinity water, pumped ahead of the micellar or alkaline chemical solution.

aulacogen

In plate tectonics, a failed rift arm. At the junctions of tectonic plates, three intersecting lithospheric plates typically are separated by "arms." Arms might be areas of rifting, convergence or transform faults (similar to a strike-slip fault). The arm along which the motion that spreads the plates apart ceases is termed the failed arm, or aulacogen. Spreading or rifting along the other arms of the triple junction can form new oceanic basins, whereas the aulacogen can become a sediment-filled graben.

condensed section

In sequence stratigraphy, a section of fine-grained sedimentary rocks that accumulated slowly, thereby representing a considerable span of time by only a thin layer. In condensed sections, fossils and organic, phosphatic and glauconitic material tend to be concentrated compared with rapidly deposited sections that contain few fossils. Condensed sections are most commonly deposited during transgressions. In such cases they are associated with "maximum flooding surfaces" and form important sequence stratigraphic markers.

The mobility of the oil is defined ahead of the displacement front while that of the injectant is defined behind the displacement front, so the respective effective permeability values are evaluated at different saturations.

In the calculation of mobility ratio, where are the mobilities of the oil and injectant assessed?

crop out

In the case of a body of rock, to be exposed at the surface of the Earth. Construction of highways and other man-made facilities and resultant removal of soil and rock has created spectacular outcrops in some regions.

in situ

In the original location or position, such as a large outcrop that has not been disturbed by faults or landslides. Tests can be performed in situ in a reservoir to determine its pressure and temperature and fluid properties.

hydration

Incorporation of water into the atomic structure of a mineral, i.e., the chemical combination of water and another substance. Gypsum is a hydrate mineral. Its anhydrous equivalent is anhydrite.

Breakout Tongs

Large capacity self-locking wrenches used to grip drillstring components and apply torque. They are the active wrenches during breakout operations. A similar set of tongs is tied off to a deadline anchor during breakout operations to provide backup to the connection, not unlike the way a plumber uses two pipe wrenches in an opposing manner to tighten or loosen water pipes, except that these are much larger.

makeup tongs

Large-capacity, self-locking wrenches used to grip drillstring components and apply torque which are active during tightening operations. As with opposing pipe wrenches for a plumber, the tongs must be used in opposing pairs. As a matter of efficiency, one set of tongs is essentially tied off with a cable or chain to the derrick, and the other is actively pulled with mechanical catheads.

tongs

Large-capacity, self-locking wrenches used to grip drillstring components and apply torque. As with opposing pipe wrenches for a plumber, the tongs must be used in opposing pairs.

down dip

Located down the slope of a dipping plane or surface. In a dipping (not flat-lying) hydrocarbon reservoir that contains gas, oil and water, the gas is updip, the gas-oil contact is downdip from the gas, and the oil-water contact is still farther downdip.

downdip

Located down the slope of a dipping plane or surface. In a dipping (not flat-lying) hydrocarbon reservoir that contains gas, oil and water, the gas is updip, the gas-oil contact is downdip from the gas, and the oil-water contact is still farther downdip.

updip

Located up the slope of a dipping plane or surface. In a dipping (not flat-lying) hydrocarbon reservoir that contains gas, oil and water, the gas is updip, the gas-oil contact is downdip from the gas, and the oil-water contact is still farther downdip.

tectonic environment

Location relative to the boundary of a tectonic plate, particularly a boundary along which plate tectonic activity is occurring or has occurred.

alluvium

Material deposited in an alluvial environment, typically detrital sediments that are poorly sorted.

Impressed current anodes

Materials to provide cathodic protection. Relatively inert to corrosion they require an external power source to generate the electric current that will bring cathodic protection to the structure.

naturally occurring radioactive materials (NORM)

Materials typically found in certain types of barium or strontium scales that may be deposited in the wellbore or production tubulars.

Galvanic anodes

Materials used to provide cathodic protection. These are made of metals such as zinc, magnesium or aluminum, which corrode more easily than the structure, thus developing enough electric current flow through the electrolyte

autochthon

Materials, especially rock masses, that formed in their present location and have not been transported. Fault surfaces can separate indigenous rocks from allochthonous rocks, although some allochthonous rocks are clearly delineated by their differing composition.

extended reach drilling

Mobil Oil Company first used this term in the early 1980s for drilling directional wells in which the drilled horizontal reach (HR) attained at total depth (TD) exceeded the true vertical depth (TVD) by a factor greater than or equal to two. Extended-reach drilling (ERD) is particularly challenging for directional drilling and requires specialized planning to execute well construction.

casing reciprocation

Movement applied to the casing string during the cementing operation to help in removal of drilling fluidand efficient placement of the cement slurry.

radial faulting

Multiple faults whose fault planes strike outward from a common center. Such faults typically are associated with salt domes, impact craters or volcanoes.

Spud

Name given to start the well drilling process by removing rock, dirt and other sedimentary material with the drill bit

Backing Off , Back Off

Name this procedure. The drillstring, including drillpipe and the bottomhole assembly, are coupled by various threadforms known as connections, or tool joints. Often when a drillstring becomes stuck it is necessary to apply this procedure so that the string can reach as deep as possible to recover as much of the string as possible. To facilitate the fishing or recovery operation, this procedure is usually accomplished by applying reverse torque and detonating an explosive charge inside a selected threaded connection.

Polyacrylamide and xantham

Name two polymers frequently used in polymer flooding.

Reservoir drive mechanisms

Natural forces in the reservoir that displace hydrocarbons out of the reservoir into the wellbore and up to surface.

wet gas

Natural gas that contains less methane (typically less than 85% methane) and more ethane and other more complex hydrocarbons.

dry gas

Natural gas that occurs in the absence of condensate or liquid hydrocarbons, or gas that has had condensable hydrocarbons removed. Dry gas typically has a gas-to-oil ratio exceeding 100,000 scf/STB.

coal bed methane

Natural gas, predominantly methane [CH4], generated during coal formation and adsorbed in coal. Natural gas adsorbs to the surfaces of matrix pores within the coal and natural fractures, or cleats, as reservoir pressure increases.

coal seam gas

Natural gas, predominantly methane [CH4], generated during coal formation and adsorbed in coal. Natural gas adsorbs to the surfaces of matrix pores within the coal and natural fractures, or cleats, as reservoir pressure increases.

coal-bed methane

Natural gas, predominantly methane [CH4], generated during coal formation and adsorbed in coal. Natural gas adsorbs to the surfaces of matrix pores within the coal and natural fractures, or cleats, as reservoir pressure increases.

coal-seam gas

Natural gas, predominantly methane [CH4], generated during coal formation and adsorbed in coal. Natural gas adsorbs to the surfaces of matrix pores within the coal and natural fractures, or cleats, as reservoir pressure increases.

coalbed methane

Natural gas, predominantly methane [CH4], generated during coal formation and adsorbed in coal. Natural gas adsorbs to the surfaces of matrix pores within the coal and natural fractures, or cleats, as reservoir pressure increases.

bitumen

Naturally-occurring, inflammable organic matter formed from kerogen in the process of petroleum generation that is soluble in carbon bisulfide. This includes hydrocarbons such as asphalt and mineral wax. Typically solid or nearly so, brown or black, bitumen has a distinctive petroliferous odor. Laboratory dissolution with organic solvents allows determination of the amount of bitumen in samples, an assessment of source rock richness.

tight oil

Oil found in relatively impermeable reservoir rock. Production of tight oil comes from very low permeability rock that must be stimulated using hydraulic fracturing to create sufficient permeability to allow the mature oil and/or natural gas liquids to flow at economic rates.

Trapped oil

Oil in pore spaces that cannot be moved because of capillary forces.

shale oil

Oil obtained by artificial maturation of oil shale. The process of artificial maturation uses controlled heating, or pyrolysis, of kerogen to release the shale oil.

Enhanced oil recovery

Oil recovery through injection of materials not normally present in the reservoir

softline

Oilfield slang term for rope not made of steel, such as nylon, cotton, or especially standard manila hemp rope.

Texas deck

On an offshore jackup drilling rig, the deck below the rotary table and rig floor where workers can access the BOP stack. This platform surrounds the base of the BOP stack and is suspended from the cantilever (where the rig floor is located) by adjustable cables. It is accessed from the main deck of the jackup barge by a semipermanent stairwell.

weight indicator

One of the instruments that the driller uses to monitor and improve the operating efficiencies of the drilling operation.

metamorphic

One of three main classes of rock. These rocks form from the alteration of preexisting rocks by changes in ambient temperature, pressure, volatile content, or all of these. Such changes can occur through the activity of fluids in the Earth and movement of igneous bodies or regional tectonic activity. The texture of metamorphic rocks can vary from almost homogeneous, or nonfoliated, to foliated rocks with a strong planar fabric or foliation produced by alignment of minerals during recrystallization or by reorientation. Common foliated metamorphic rocks include gneiss, schist and slate. Marble, or metamorphosed limestone, can be foliated or non-foliated. Hornfels is a nonfoliated metamorphic rock. Graphite, chlorite, talc, mica, garnet and staurolite are distinctive metamorphic minerals.

outside diameter (OD)

Outer diameter. Casing and tubing are commonly described in terms of inside diameter (ID) and outside diameter.

aeolian

Pertaining to the environment of deposition of sediments by wind, such as the sand dunes in a desert. Because fine-grained sediments such as clays are removed easily from wind-blown deposits, eolian sandstones are typically clean and well-sorted.

detritus

Particles of rock derived from the mechanical breakdown of preexisting rocks by weathering and erosion. Detrital fragments can be transported to recombine and, through the process of lithification, become sedimentary rocks. Detrital is usually used synonymously with clastic, although a few authors differentiate between weathering of particles, which forms detrital sediments, and mechanical breakage, which produces clastic sediments.

Hydrophobic

Pertaining to a "dislike" for water by the surface of a material or a molecule.

Immiscible

Pertaining to a condition in which two fluids are incapable of forming molecularly distributed mixtures or attaining homogeneity at that scale. The fluids separate into two phases with an interface between them.

immiscible

Pertaining to a condition in which two fluids are incapable of forming molecularly distributed mixtures or attaining homogeneity at that scale. The fluids separate into two phases with an interface between them. For example, oil and water are immiscible.

Miscible

Pertaining to a condition in which two or more fluids can mix in all proportions and form a single homogeneous phase.

miscible

Pertaining to a condition in which two or more fluids can mix in all proportions and form a single homogeneous phase.

cross-sectional

Pertaining to a diagram of a vertical section through a volume, as opposed to the surface, "bird's eye," or plan view of a map. Cross sections are useful for displaying the types and orientations of subsurface structures and formations.

diatomaceous

Pertaining to a diatom, which is a microscopic, single-celled, freshwater or saltwater algae that has a silica-rich cell wall called a frustule. Diatoms are so abundant that they can form thick layers of sediment composed of the frustules of the organisms that died and sank to the bottom. Frustules have been an important component of deep-sea deposits since Cretaceous time. Diatomite is the sedimentary rock that forms from diatom frustules.

hiatal

Pertaining to a hiatus, a cessation in deposition of sediments during which no strata form or an erosional surface forms on the underlying strata; a gap in the rock record. This period might be marked by development of a lithified sediment (hardground) or burrowed surface characteristic of periods when sea level was relatively low. A disconformity can result from a hiatus.

overmature

Pertaining to a hydrocarbon source rock that has generated as much hydrocarbon as possible and is becoming thermally altered.

immature

Pertaining to a hydrocarbon source rock that has not fully entered optimal conditions for generation.

orogenic

Pertaining to a major episode of plate tectonic activity in which lithospheric plates collide and produce mountain belts, in some cases including the formation of subduction zones and igneous activity. Thrust faults and folds are typical geological structures seen in areas of orogeny.

plastic

Pertaining to a material that can deform permanently without rupturing.

elastic

Pertaining to a material that can undergo stress, deform, and then recover and return to its original shape after the stress ceases. Once stress exceeds the yield stress or elastic limit of a material, permanent deformation occurs and the material will not return to its original shape once the stress is removed. In some materials, including rocks, elastic behavior depends on the temperature and the duration of the stress as well as its intensity.

impermeable

Pertaining to a rock that is incapable of transmitting fluids because of low permeability. Shale has a high porosity, but its pores are small and disconnected, so it is relatively impermeable. Impermeable rocks are desirable sealing rocks or cap rocks for reservoirs because hydrocarbons cannot pass through them readily.

clean

Pertaining to a sedimentary rock, such as sandstone or limestone, that contains only minimal amounts of clay minerals. These reservoir rocks typically have better porosity and permeability than dirty rocks whose pores are clogged with fine clay particles. Clean and dirty are qualitative, descriptive terms.

dextral

Pertaining to a strike-slip fault or right-lateral fault in which the block across the fault moves to the right. If it moves left, the relative motion is described as sinistral. Clockwise rotation or spiraling is also described as dextral.

sinistral

Pertaining to a strike-slip or left-lateral fault in which the block across the fault moves to the left; also called a sinistral strike-slip fault. If it moves to the right, the relative motion is described as dextral. Counterclockwise rotation or spiraling is also described as sinistral.

cataclastic

Pertaining to a type of metamorphic rock with shearing and granulation of minerals caused by high mechanical stress during faulting or dynamic metamorphism, typically during episodes of plate tectonic activity.

multilateral

Pertaining to a well that has more than one branch radiating from the mainborehole. The term is also used to refer to the multilateral well itself.

anticlinal

Pertaining to an anticline, an arch-shaped fold in rock in which rock layers are upwardly convex. The oldest rock layers form the core of the fold, and outward from the core progressively younger rocks occur. Anticlines form many excellent hydrocarbon traps, particularly in folds with reservoir-quality rocks in their core and impermeable seals in the outer layers of the fold. A syncline is the opposite type of fold, having downwardly convex layers with young rocks in the core.

eolian

Pertaining to the environment of deposition of sediments by wind, such as the sand dunes in a desert. Because fine-grained sediments such as clays are removed easily from wind-blown deposits, eolian sandstones are typically clean and well-sorted.

nipple up

The process of assembling well-control or pressure-control equipment on the wellhead.

deltaic

Pertaining to an area of deposition or the deposit formed by a flowing sediment-laden current as it enters an open or standing body of water, such as a river spilling into a gulf. As a river enters a body of water, its velocity drops and its ability to carry sediment diminishes, leading to deposition. The term has origins in Greek because the shape of deltas in map view can be similar to the Greek letter delta. The shapes of deltas are subsequently modified by rivers, tides and waves. There is a characteristic coarsening upward of sediments in a delta. The three main classes of deltas are river-dominated (Mississippi River), wave-dominated (Nile River), and tide-dominated (Ganges River). Ancient deltas contain some of the largest and most productive petroleum systems.

Lipophilic

Pertaining to an attraction for oil by a surface of a material or a molecule. This term is applied to the oil-wetting behavior of treatment chemicals for oil muds.

Hydrophilic

Pertaining to an attraction for water by the surface of a material or a molecule.

littoral

Pertaining to an environment of deposition affected by tides, the area between high tide and low tide. Given the variation of tides and land forms from place to place, geologists describe littoral zones locally according to the fauna capable of surviving periodic exposure and submersion.

fluvial

Pertaining to an environment of deposition by a river or running water. Fluvial deposits tend to be well sorted, especially in comparison with alluvial deposits, because of the relatively steady transport provided by rivers.

lacustrine

Pertaining to an environment of deposition in lakes, or an area having lakes. Because deposition of sediment in lakes can occur slowly and in relatively calm conditions, organic-rich source rocks can form in lacustrine environments.

estuarine

Pertaining to an estuary, a semi-enclosed coastal environment of deposition in which a river mouth permits freshwater to contact and mix with seawater.

through-tubing

Pertaining to any reservoir or wellbore treatment performed through the tubing string. are generally associated with live-well operations, thereby causing minimal interruption to production and eliminating the need to kill the well.

biostratigraphic

Pertaining to biostratigraphy, the application of plant and animal fossils to date and correlate strata in order to elucidate Earth history, combining the principles of paleontology and stratigraphy. In the petroleum industry, biostratigraphy often denotes the use of terrestrial (pollen and spores) and marine (diatoms, foraminifera, nannofossils) microfossils to determine the absolute or relative age and depositional environment of a particular formation, source rock or reservoir of interest.

sweet

Pertaining to crude oil or natural gas lacking appreciable amounts of sulfur or sulfur compounds.

diagenetic

Pertaining to diagenesis, which is the physical, chemical or biological alteration of sediments into sedimentary rock at relatively low temperatures and pressures that can result in changes to the rock's original mineralogy and texture. After deposition, sediments are compacted as they are buried beneath successive layers of sediment and cemented by minerals that precipitate from solution. Grains of sediment, rock fragments and fossils can be replaced by other minerals during diagenesis. Porosity usually decreases during diagenesis, except in rare cases such as dissolution of minerals and dolomitization. Diagenesis does not include weathering processes. Hydrocarbon generation begins during diagenesis. There is not a clear, accepted distinction between diagenesis and metamorphism, although metamorphism occurs at pressures and temperatures higher than those of the outer crust, where diagenesis occurs

upstream

Pertaining to equipment, facilities or systems located in the wellbore or production train above the surface choke or Christmas tree.

down stream

Pertaining to equipment, facilities or systems that are located in the production train after the surfacechoke, typically attached or close to the Christmas tree.

downstream

Pertaining to equipment, facilities or systems that are located in the production train after the surfacechoke, typically attached or close to the Christmas tree.

eustatic

Pertaining to eustasy, a term for global sea level and its variations. Changes in sea level can result from movement of tectonic plates altering the volume of ocean basins, or when changes in climate affect the volume of water stored in glaciers and in polar icecaps. Eustasy affects positions of shorelines and processes of sedimentation, so interpretation of eustasy is an important aspect of sequence stratigraphy.

evaporitic

Pertaining to evaporite, a class of sedimentary minerals and sedimentary rocks that form by precipitation from evaporating aqueous fluid. Common evaporite minerals are halite, gypsum and anhydrite, which can form as seawater evaporates, and the rocks limestone and dolostone. Certain evaporite minerals, particularly halite, can form excellent cap rocks or seals for hydrocarbon traps because they have minimal porosity and they tend to deform plastically (as opposed to brittle fracturing that would facilitate leakage).

exploratory

Pertaining to exploration, the initial phase in petroleum operations that includes generation of a prospect or play or both, and drilling of an exploration well. Appraisal, development and production phases follow successful exploration.

geological

Pertaining to geology, the study of the Earth-its history, structure, composition, life forms and the processes that continue to change it.

hydrothermal

Pertaining to hot fluids, particularly hot water, or the activity of hot water, or precipitates thereof. Hydrothermal alteration can change the mineralogy of rock, producing different minerals, including quartz, calcite and chlorite. Hydrothermal activity is commonly associated with hot water that accompanies, or is heated by, magma.

convergent

Pertaining to the movement of tectonic plates toward each other, generating compressional forces and ultimately resulting in collision, and in some cases subduction, of tectonic plates. The boundary where tectonic plates converge is called a convergent margin.

profile modification

The process of controlling undesirable water production from a well by conducting treatments to preventconing or cresting.

allochthonous

Pertaining to materials, particularly rock masses, that formed somewhere other than their present location, and were transported by fault movements, large-scale gravity sliding, or similar processes. Autochthonous material, in contrast, formed in its present location. Landslides can result in large masses of allochthonous rock, which typically can be distinguished from autochthonous rocks on the basis of their difference in composition. Faults and folds can also separate allochthons from autochthons.

felsic

Pertaining to minerals or igneous rocks composed of minerals such as quartz and feldspar that are relatively light in color and density. The word comes from the terms feldspar and silica. Granite is a felsic igneous rock. (Compare with mafic.)

mafic

Pertaining to minerals or igneous rocks composed of minerals that are rich in iron and magnesium, dense, and typically dark in color. The term comes from the words magnesium and ferric. Common mafic minerals are olivine and pyroxene. Basalt is a mafic igneous rock. (Compare with felsic.)

authigenic

Pertaining to minerals or materials that grow in place with a rock, rather than having been transported and deposited. These include quartz, chlorite and other pore-filling minerals or cements that grow during diagenesis. Evaporite minerals are authigenic, or formed in situ.

allogenic

Pertaining to minerals or rock fragments that formed in one location but were transported to another location and deposited. Clastic sediments in a rock such as sandstone are allogenic, or formed elsewhere.

igneous

Pertaining to one of three main classes of rocks. These rocks crystallize from molten rock, or magma, with interlocking mineral crystals. Igneous rocks that crystallize slowly, typically below the surface of the Earth, are plutonic igneous rocks and have large crystals (large enough to see with the naked eye). Volcanic igneous rocks crystallize quickly at the Earth's surface and have small crystals (usually too small to see without magnification). Common examples include granite (plutonic) and rhyolite (volcanic), diorite (plutonic) and andesite (volcanic), and gabbro (plutonic) and basalt (volcanic). Igneous rocks typically comprise the minerals quartz, mica, feldspar, amphibole, pyroxene and olivine.

detrital

Pertaining to particles of rock derived from the mechanical breakdown of preexisting rocks by weathering and erosion. Detrital fragments can be transported to recombine and, through the process of lithification, become sedimentary rocks. Detrital is usually used synonymously with clastic, although a few authors differentiate between weathering of particles, which forms detrital sediments, and mechanical breakage, which produces clastic sediments.

porous

Pertaining to rocks that incorporate pores or void spaces, which can contain air, water, hydrocarbons or other fluids. In a body of rock, the percentage of pore space is the porosity. Porosity can be a relic of deposition (primary porosity, such as space between grains that were not compacted together completely) or can develop through alteration of the rock (secondary porosity, such as when feldspar grains or fossils are preferentially dissolved from sandstones). Porosity can be generated by the development of fractures, in which case it is called fracture porosity. Effective porosity is the interconnected pore volume in a rock that contributes to fluid flow in a reservoir. It excludes isolated pores. Total porosity is the total void space in the rock whether or not it contributes to fluid flow. Thus, effective porosity is typically less than total porosity. Shale gas reservoirs tend to have relatively high porosity, but the alignment of platy grains such as clays makes their permeability very low.

marine

Pertaining to sediments or environments in seas or ocean waters, between the depth of low tide and the ocean bottom.

consolidated

Pertaining to sediments that have been compacted and cemented to the degree that they become coherent, relatively solid rock. Typical consequences of consolidation include an increase in density and acoustic velocity, and a decrease in porosity.

incompetent

Pertaining to strata that are relatively ductile and tend to flow under stress rather than deform by brittle faulting or fracturing. The bed thickness of incompetent beds tends to change during deformation.

disharmonic

Pertaining to structures in which the shapes of adjacent layers differ or do not conform to one another. Folds of rock layers that have different mechanical properties or competence tend to be disharmonic, with a change in fold shape, symmetry or wavelength from one layer to the next.

harmonic

Pertaining to structures in which the shapes of adjacent layers resemble or conform to one another. Folds of rock layers that have similar mechanical properties or competence tend to be harmonic, with little change in fold shape, symmetry or wavelength from one layer to the next.

volcanic

Pertaining to surface features of the Earth that allow magma, ash and gas to erupt. The vent can be a fissure or a conical structure.

water wet

Pertaining to the adhesion of a liquid to the surface of a solid. In '' '' conditions, a thin film of water coats the surface of the formation matrix, a condition that is desirable for efficient oil transport. Treatments that change the wettability of the formation to oil-wet can significantly impair productivity.

azimuthal

Pertaining to the angle between the vertical projection of a line of interest onto a horizontal surface and true north or magnetic north measured in a horizontal plane, typically measured clockwise from north.

abyssal

Pertaining to the depositional environment of the deepest area of the ocean basins, the abyss. The depositional energy is low, the abyssal plain is flat and nearly horizontal, and fine-grained sediments are deposited slowly by waning turbidity currents or from suspension in the water. The water is thousands of meters deep (> 2000 m) [6520 ft], so the water is cold and sunlight is minimal.

benthic

Pertaining to the environment and conditions of organisms living at the water bottom, or benthos. Also called benthonic.

bathyal

Pertaining to the environment of deposition and the organisms of the ocean between depths of 200 m [656 ft], the edge of the continental shelf, and 2000 m [6560 ft]. The bathyal environment is intermediate between the neritic environment and the abyss.

Bottoms Up

Pertaining to the mud and cuttings that are calculated or measured to come from the bottom of the hole since the start of circulation. Circulation may be initiated after a static period, such as a trip, or from a given depth while drilling. This latter type is particularly useful to mud loggers and others trying to discern the lithology being drilled.

Oil-wet

Pertaining to the preference of a solid to be in contact with an oil phase rather than a water or gas phase.

alluvial

Pertaining to the subaerial (as opposed to submarine) environment, action and products of a stream or river on its floodplain, usually consisting of detrital clastic sediments, and distinct from subaqueous deposition such as in lakes or oceans and lower energy fluvial deposition. Sediments deposited in an alluvial environment can be subject to high depositional energy, such as fast-moving flood waters, and may be poorly sorted or chaotic.

through flowline (TFL)

Pertaining to treatments performed on subsea wells where the fluids and associated pump-down equipment, such as plugs or darts, are pumped through the flowline normally used for production fluids

vesicular

Pertaining to vesicles, bubble-shaped cavities in volcanic rock formed by expansion of gas dissolved in the precursor magma.

high-pressure, high-temperature OR HPHT

Pertaining to wells that are hotter or higher pressure than most.

homogeneous

Possessing the quality of uniformity. If irregularities are distributed evenly in a material, the material is homogeneous. (Compare with heterogeneous.)

heterogeneous

Possessing the quality of variation in rock properties with location in a reservoir or formation. Shale gas reservoirs are heterogeneous formations whose mineralogy, organic content, natural fractures, and other properties vary from place to place. This heterogeneity makes petroleum system modeling, formation evaluation, and reservoir simulation critical to maximizing production from shale reservoirs.

aeolotropy

Predictable variation of a property of a material with the direction in which it is measured, which can occur at all scales. For a crystal of a mineral, variation in physical properties observed in different directions is aeolotropy (also known as anisotropy). In rocks, variation in seismic velocity measured parallel or perpendicular to bedding surfaces is a form of aeolotropy. Often found where platy minerals such as micas and clays align parallel to depositional bedding as sediments are compacted, aeolotropy is common in shales.

anisotropy

Predictable variation of a property of a material with the direction in which it is measured, which can occur at all scales. For a crystal of a mineral, variation in physical properties observed in different directions is anisotropy. In rocks, variation in seismic velocity measured parallel or perpendicular to bedding surfaces is a form of anisotropy. Often found where platy minerals such as micas and clays align parallel to depositional bedding as sediments are compacted, anisotropy is common in shales.

fossil

Preserved remnants of plants or animals, such as skeletons, shells, casts or molds, tracks or borings, and feces.

formation fracture pressure

Pressure above which injection of fluids will cause the rock formation to fracture hydraulically

gas bearing

Relating to a formation or interval containing gas, either dissolved in the formation fluid or as free gas. The term is occasionally used to describe wellbore fluids containing dissolved gas.

gas-bearing

Relating to a formation or interval containing gas, either dissolved in the formation fluid or as free gas. The term is occasionally used to describe wellbore fluids containing dissolved gas.

parasequence

Relatively conformable depositional units bounded by surfaces of marine flooding, surfaces that separate older strata from younger and show an increase in water depth in successively younger strata. Parasequences are usually too thin to discern on seismic data, but when added together, they form sets called parasequence sets that are visible on seismic data.

Abnormal Pressure

Reservoir pore fluid pressure that is not similar to normal saltwater gradient pressure. This term is usually associated with higher than normal pressure, increased complexity for the well designer and an increased risk of well control problems

recycled gas

Residual gas that remains entrained in the drilling fluid despite being circulated to surface. At the surface, it remains in the mudstream, which is suctioned from the mud pit and recirculated into the wellbore.

cuttings

Small pieces of rock that break away due to the action of the bit teeth.

cuttings

Small pieces of rock that break away due to the action of the bit teeth. These are screened out of the liquid mud system at the shale shakers and are monitored for composition, size, shape, color, texture, hydrocarbon content and other properties by the mud engineer, the mud logger and other on-site personnel.

ball sealers

Small spheres designed to seal perforations that are accepting the most fluid, thereby diverting reservoir treatments to other portions of the target zone. Ball sealers are incorporated into the treatment fluid and pumped with it. The effectiveness of this type of mechanical diversion to keep the balls in place is strongly dependent on the differential pressure across the perforation and the geometry of the perforation itself.

injectite

Structures formed by sediment injection. Because they resemble intrusive and extrusive igneous features, much of the vocabulary for describing injectites, or clastic intrusions, comes from igneous geology. Sills are emplaced parallel to bedding, whereas dikes cut through bedding. The strata containing the intrusion are called host strata and the layers that feed the intrusion are the parent beds. Sand-injection features exhibit size scales from millimeters to kilometers, and have been seen in cores, borehole image logs, seismic sections, outcrops, aerial photographs and satellite images.

systems tract

Subdivisions of sequences that consist of discrete depositional units that differ in geometry from other systems tracts and have distinct boundaries on seismic data. Different systems tracts are considered to represent different phases of eustatic changes. A lowstand systems tract develops during times of relatively low sea level; a highstand systems tract at times of high sea level; and a transgressive systems tract at times of changing sea level.

geopressured

Subject to the pressure within the Earth, or formation pressure. The common oilfield usage, however, is to indicate anomalous subsurface pore pressure that is higher or lower than the normal, predicted hydrostatic pressure for a given depth, or the pressure exerted per unit area by a column of fresh water from sea level to a given depth. Abnormally low pore pressure might occur in areas where fluids have been drained, such as a depleted hydrocarbon reservoir. Abnormally high pore pressure might occur in areas where burial of water-filled sediments by an impermeable sediment such as clay was so rapid that fluids could not escape and the pore pressure increased with deeper burial.

overpressure

Subsurface pressure that is abnormally high, exceeding hydrostatic pressure at a given depth. The term geopressure is commonly, and incorrectly, used synonymously. Abnormally high pore pressure can occur in areas where burial of fluid-filled sediments is so rapid that pore fluids cannot escape, so the pressure of the pore fluids increases as overburden increases. Drilling into overpressured strata can be hazardous because overpressured fluids escape rapidly, so careful preparation is made in areas of known overpressure.

effective permeability

The ability to preferentially flow or transmit a particular fluid when other immiscible fluids are present in the reservoir (e.g., effective permeability of gas in a gas-water reservoir). The relative saturations of the fluids as well as the nature of the reservoir affect the effective permeability. In contrast, absolute permeability is the measurement of the permeability conducted when a single fluid or phase is present in the rock.

permeability

The ability, or measurement of a rock's ability, to transmit fluids, typically measured in darcies or millidarcies. The term was basically defined by Henry Darcy, who showed that the common mathematics of heat transfer could be modified to adequately describe fluid flow in porous media. Formations that transmit fluids readily, such as sandstones, are described as permeable and tend to have many large, well-connected pores. Impermeable formations, such as shales and siltstones, tend to be finer grained or of a mixed grain size, with smaller, fewer, or less interconnected pores. Absolute permeability is the measurement of the permeability conducted when a single fluid, or phase, is present in the rock. Effective permeability is the ability to preferentially flow or transmit a particular fluid through a rock when other immiscible fluids are present in the reservoir (for example, effective permeability of gas in a gas-water reservoir). The relative saturations of the fluids as well as the nature of the reservoir affect the effective permeability. Relative permeability is the ratio of effective permeability of a particular fluid at a particular saturation to absolute permeability of that fluid at total saturation. If a single fluid is present in a rock, its relative permeability is 1.0. Calculation of relative permeability allows for comparison of the different abilities of fluids to flow in the presence of each other, since the presence of more than one fluid generally inhibits flow.

retrogradation

The accumulation of sequences by deposition in which beds are deposited successively landward because sediment supply is limited and cannot fill the available accommodation. Thus, the position of the shoreline migrates backward onto land, a process called transgression, during episodes of retrogradation.

aggradation

The accumulation of stratigraphic sequences by deposition that stacks beds atop each other, building upwards during periods of balance between sediment supply and accommodation.

trip

The act of pulling the drillstring out of the hole or replacing it in the hole

tripping pipe

The act of pulling the drillstring out of the hole or replacing it in the hole. A pipe trip is usually done because the bit has dulled or has otherwise ceased to drill efficiently and must be replaced.

pipe trip OR tripping pipe

The act of pulling the drillstring out of the hole or replacing it in the hole. Usually done because the bit has dulled or has otherwise ceased to drill efficiently and must be replaced.

snub

The act of putting drillpipe into the wellbore when the blowout preventers (BOPs) are closed and pressure is contained in the well. This action is necessary when a kick is taken, since well kill operations should always be conducted with the drillstring on bottom, and not somewhere up the wellbore. In these kind of operations, the pressure in the wellbore acting on the cross-sectional area of the tubular can exert sufficient force to overcome the weight of the drillstring, so the string must be pushed (or "snubbed") back into the wellbore. Otherwise, in ordinary stripping operations, the pipe falls into the wellbore under its own weight, and no additional downward force or pushing is required. If only the annular BOP has been closed, the drillpipe may be slowly and carefully lowered into the wellbore, and the BOP itself will open slightly to permit the larger diameter tool joints to pass through. If the well has been closed with the use of ram BOPs, the tool joints will not pass by the closed ram element. Hence, while keeping the well closed with either another ram BOP or the annular BOP, the ram must be opened manually, then the pipe lowered until the tool joint is just below the ram, and then closing the ram again. This procedure is repeated whenever a tool joint must pass by a ram BOP.

stripping

The act of putting drillpipe into the wellbore when the blowout preventers (BOPs) are closed and pressure is contained in the well. This is necessary when a kick is taken, since well kill operations should always be conducted with the drillstring on bottom, and not somewhere up the wellbore. In ordinary ____________ operations, the pipe falls into the wellbore under its own weight, and no additional downward force or pushing is required. It differs from snubbing operations in that during snubbing, the pressure in the wellbore acting on the cross-sectional area of the tubular can exert sufficient force to overcome the weight of the drillstring, so the string must be pushed (or "snubbed") back into the wellbore. When there is a kick, if only the annular BOP has been closed, the drillpipe may be slowly and carefully lowered into the wellbore, and the BOP itself will open slightly to permit the larger diameter tool joints to pass through. If the well has been closed with the use of ram BOPs, the tool joints will not pass by the closed ram element. Hence, while keeping the well closed with either another ram BOP or the annular BOP, the ram must be opened manually, then the pipe lowered until the tool joint is just below the ram, and then closing the ram again. This procedure is repeated whenever a tool joint must pass by a ram BOP.

Casing Head

The adapter between the first casing string and either the BOP stack (during drilling) or the wellhead (after completion). This adapter may be threaded or welded onto the casing, and may have a flanged or clamped connection to match the BOP stack or wellhead

casing head

The adapter between the first casing string and either the BOP stack (during drilling) or the wellhead(after completion). This adapter may be threaded or welded onto the casing, and may have a flanged or clamped connection to match the BOP stack or wellhead.

Infill drilling

The addition of wells in a field that decreases average well spacing. This practice both accelerates expected recovery and increases estimated ultimate recovery in heterogeneous reservoirs by improving the continuity between injectors and producers. As well spacing is decreased, the shifting well patterns alter the formation-fluid flow paths and increase sweep to areas where greater hydrocarbon saturations exist.

shear strain

The amount of deformation by shearing, in which parallel lines slide past each other in differing amounts. The measurement is expressed as the tangent of the change in angle between lines that were initially perpendicular.

biostratigraphy

The application of plant and animal fossils to date and correlate strata in order to elucidate Earth history, combining the principles of paleontology and stratigraphy. In the petroleum industry, this often denotes the use of terrestrial (pollen and spores) and marine (diatoms, foraminifera, nannofossils) microfossils to determine the absolute or relative age and depositional environment of a particular formation, source rock or reservoir of interest.

relative age

The approximate age determination of rocks, fossils or minerals made by comparing whether the material is younger or older than other surrounding material. Relative age is estimated according to stratigraphic and structural relationships, such as superposition, and by fossil content, since the relative ages and successions of fossils have been established by paleontologists. The measurement of the decay of radioactive isotopes, especially uranium, rubidium, argon and carbon, has allowed geologists to more precisely determine the age in years of rock formations, known as the absolute age. Tree rings and seasonal sedimentary deposits called varves can be counted to determine absolute age. Although the term implies otherwise, "absolute" ages typically have some amount of potential error and are inexact.

free water

The aqueous phase that separates from a slurry or mixture of fluids. In cementing operations,''' '''' is undesirable since channels tend to form through the set cement, providing potential gas migrationpaths. When processing reservoir fluids, the water that separates easily under gravity separation is known as '' '''. In some cases, additional water may be locked in an emulsion, contributing to the aqueous phase but not available as '''' ''''.

continental shelf

The area at the edges of a continent from the shoreline to a depth of 200 m [660 ft], where the continental slope begins. The shelf is commonly a wide, flat area with a slight seaward slope. The term is sometimes used as a for platform.

shelf

The area at the edges of a continent from the shoreline to a depth of 200 m [660 ft], where the continental slope begins. The shelf is commonly a wide, flat area with a slight seaward slope. The term is sometimes used as a for platform.

depositional environment

The area in which and physical conditions under which sediments are deposited, including sediment source; depositional processes such as deposition by wind, water or ice; and location and climate, such as desert, swamp or river.

depocenter

The area of thickest deposition in a basin.

damaged zone

The area surrounding the wellbore that has been harmed by the drilling process, generally as a result of mud or cement-filtrate invasion. Near-wellbore damage can significantly affect productivity and is typically easier to prevent than it is to cure. Although almost always present, a lightly damaged zone around the wellbore can be bypassed by perforation tunnels to create connecting conduits from the wellbore to the undamaged reservoir formation. More severe cases of damage may require a matrix-acidizing treatment to restore the natural permeability, or a hydraulic fracturing treatment to create a new high-conductivity flow path to the reservoir.

cubic packing

The arrangement in space of uniform spheres (atoms and molecules in mineral crystals, or grains in clastic sedimentary rocks) that results in a cubic material structure. Cubic packing is mechanically unstable, but it is the most porous packing arrangement, with about 47% porosity in the ideal situation. Most sediments are not uniform spheres of the same size, nor can they be arranged in a cubic structure naturally, so most sediments have much less than 47% porosity.

Mohorovicic discontinuity

The boundary between the crust and the mantle of the Earth, which varies from approximately 5 km [3 miles] under the midoceanic ridges to 75 km [46 miles] deep under the continents. This boundary, commonly called "the Moho," was recognized in 1909 by Croatian seismologist Andrija Mohorovicic on the basis of its abruptly higher compressional wave (P-wave) velocity.

area open to flow

The calculated flow area provided by perforations across a specific zone of interest. The resulting value is used to calculate pressure drops and fluid-flow performance.

conductor pipe

The casing string that is usually put into the well first, particularly on land wells, to prevent the sides of the hole from caving into the wellbore. This casing, sometimes called drive pipe, is generally a short length and is sometimes driven into the ground.

coning

The change in oil-water contact or gas-oil contact profiles as a result ofdrawdown pressures during production. ''' occurs in vertical or slightly deviated wells and is affected by the characteristics of the fluids involved and the ratio of horizontal to vertical permeability.

cementer OR cement engineer

The colloquial term for the crew member in charge of a specialized cementing crew and trucks.

cementing engineer or cementer

The colloquial term for the crew member in charge of a specialized cementing crew and trucks.

round trip

The complete operation of removing the drillstring from the wellbore and running it back in the hole. This operation is typically undertaken when the bit becomes dull or broken, and no longer drills the rock efficiently.

Circulation System

The complete, circuitous path that the drilling fluid travels. Starting at the main rig pumps, major components include surface piping, the standpipe, the kelly hose (rotary), the kelly, the drillpipe, drill collars, bit nozzles, the various annular geometries of the openhole and casing strings, the bell nipple, the flowline, the mud-cleaning equipment, the mud tanks, the centrifugal precharge pumps and, finally, the positive displacement main rig pumps

TOC

The concentration of organic material in source rocks as represented by the weight percent of organic carbon. A value of approximately 0.5% total organic carbon by weight percent is considered the minimum for an effective source rock, although values of 2% are considered the minimum for shale gas reservoirs; values exceeding 10% exist, although some geoscientists assert that high total organic carbon values indicate the possibility of kerogen filling pore space rather than other forms of hydrocarbons. Total organic carbon is measured from 1-g samples of pulverized rock that are combusted and converted to CO or CO2. If a sample appears to contain sufficient total organic carbon to generate hydrocarbons, it may be subjected to pyrolysis.

anoxic

The condition of an environment in which free oxygen is lacking or absent.

anaerobic

The condition of an environment in which free oxygen is lacking or absent. A description of organisms that can survive in the absence of oxygen, particularly bacteria.

day rate

The daily cost to the operator of renting the drilling rig and the associated costs of personnel and routine supplies. This cost may or may not include fuel, and usually does not include capital goods, such as casing and wellheads, or special services, such as logging or cementing. In most of the world, it represents roughly half of the cost of the well.

parallel fold

The deformation of rock layers in which the thickness of each layer, measured perpendicular to initial (undeformed) layering, is maintained after the rock layers have been folded.

concentric fold

The deformation of rock layers in which the thickness of each layer, measured perpendicular to initial undeformed layering, is maintained after the rock layers have been folded.

elastic deformation

The deformation that can be recovered when an applied stress has been removed. When the elastic limit of a material has been exceeded, nonrecoverable, permanent deformation occurs.

sedimentation

The process of creation, transportation and deposition of sediments.

convection

The density- and heat-driven cycling, transfer or circulation of energy through which material initially warms up and becomes relatively less dense, then rises, cools and becomes relatively more dense, and finally sinks. As a consequence of convection, material can turn over repeatedly in a convection cell. Within the Earth, radiogenic heating results in convection appearing in the mantle and might drive plate tectonic motions. Convection also occurs in the ocean waters and in the Earth's atmosphere.

contract depth

The depth in a drilling well at which the drilling contractor receives a lump-sum payment for reaching a particular milestone. The contract depth is specified in a legal agreement between the operator, who pays for the well, and the drilling contractor, who owns and operates the drilling rig. Contract depth may be the final or total depth (TD) of the well, an intermediate point in the well or another milestone, such as running well-logging tools to the bottom of the hole.

driller's depth

The depth of a well or features within the wellbore as measured while drilling. The measured length of each joint of drillpipe or tubing is added to provide a total depth or measurement to the point of interest.''' is the first depth measurement of a wellbore and is taken from the rotary table level on therig floor. In most cases, subsequent depth measurements, such as those made during the wellcompletion phase, are corrected to the wellhead datum that is based on drillers depth.

pressure drawdown

The differential pressure that drives fluids from the reservoir into the wellbore. The ''''''', and therefore the production rate, of a producing interval is typically controlled by surface chokes. Reservoir conditions, such as the tendency to produce sand, may limit the ''''' that may be safely applied during production before damage or unwanted sand production occurs.

s.g.

The dimensionless ratio of the density of a material to that of the same volume of water. Most common minerals have specific gravities between 2 and 7.

Azimuth

The direction in which a deviated or horizontal well is drilled relative to magnetic north. Specified in Degrees.

bottomhole injection pressure (bhip)

The downhole pressure at which a treatment fluid can be injected into a zone of interest. The bottomhole injection pressure is typically calculated by adding the hydrostatic pressure of the fluid column to the surface pump pressure measured during an injection test.

bottomhole pressure

The downhole pressure, measured or calculated at a point of interest, generally the top of the perforated interval.

bottomhole temperature

The downhole temperature measured or calculated at a point of interest. The ''' without reference to circulating or static conditions, is typically associated with producing conditions.

wellbore OR borehole

The drilled hole or borehole, including the openhole or uncased portion of the well. Borehole may refer to the inside diameter of the wellbore wall, the rock face that bounds the drilled hole.

yield point

The elastic limit, or the point at which a material can no longer deform elastically. When the elastic limit is exceeded by an applied stress, permanent deformation occurs.

drilling procedure OR drilling program

The engineering plan for constructing the wellbore. The plan includes well geometries, casingprograms, mud considerations, well control concerns, initial bit selections, offset well information, porepressure estimations, economics and special procedures that may be needed during the course of the well

tool joint

The enlarged and threaded ends of joints of drillpipe. They provide high-strength, high-pressurethreaded connections that are sufficiently robust to survive the rigors of drilling and numerous cycles of tightening and loosening at threads.

measurements while drilling

The evaluation of physical properties, usually including pressure, temperature and wellbore trajectory in three-dimensional space, while extending a wellbore.

pressure hunt

The evaluation of various well parameters in an attempt to identify when the pore pressure in a drilling well is changing. A team consisting of geologists, engineers and most of the rigsite personnel usually conducts the hunt. The purpose is to detect the pore pressure transition (usually from lower to higher pressure) and safely set casing in thetransition zone to maximize wellbore strength

petrography

The examination of rocks in thin section. Rock samples can be glued to a glass slide and the rock ground to 0.03-mm thickness in order to observe mineralogy and texture using a microscope. (A petrographic microscope is a transmitted-light polarizing microscope.) Samples of sedimentary rock can be impregnated with blue epoxy to highlight porosity.

jet velocity

The exit velocity of the drilling fluid after it accelerates through bit nozzles.

primary migration

The expulsion of newly generated hydrocarbons from a source rock. The further movement of the hydrocarbons into reservoir rock in a hydrocarbon trap or other area of accumulation is secondary migration.

matrix

The finer grained, interstitial particles that lie between larger particles or in which larger particles are embedded in sedimentary rocks such as sandstones and conglomerates.

Thermal simulation

The finite-difference or finite-element reservoir simulation that includes energy equations and calculations used to describe heat conduction, heat and fluid convection, and latent heat exchanges occurring in the reservoir rock and fluids during a thermal recovery process such as steamflooding, steam assisted gravity drainage, or in-situ combustion.

Waterflood kick

The first indication of increased crude-oil production as the result of a waterflooding project.

Primary production or primary recovery

The first stage of hydrocarbon production, in which natural reservoir energy, such as gasdrive, waterdrive or gravity drainage, displaces hydrocarbons from the reservoir, into the wellbore and up to surface.

crown block

The fixed set of pulleys (called sheaves) located at the top of the derrick or mast, over which the drilling line is threaded.

crown block

The fixed set of pulleys (called sheaves) located at the top of the derrick or mast, over which the drilling line is threaded. The companion blocks to these pulleys are the traveling blocks. By using two sets of blocks in this fashion, great mechanical advantage is gained, enabling the use of relatively small drilling line (3/4 to 1 1/2 in. diameter steel cable) to hoist loads many times heavier than the cable could support as a single strand.

crossflow

The flow of fluid across the bottom of the bit after it exits the bit nozzles, strikes the bottom or sides of the hole and turns upwards to the annulus. OR The flow of reservoir fluids from one zone to another. Can occur when a lost returns event is followed by a well control event. The higher pressured reservoir fluid flows out of the formation, travels along the wellbore to a lower pressured formation, and then flows into the lower pressure formation.

packer fluid

The fluid that remains in the tubing-casing annulus above the packer after the completion has been runand all circulation devices have been isolated.

displacement fluid

The fluid, usually drilling mud, used to force a cement slurry out of the casing string and into theannulus.

axial loading

The force acting along the axis of an object. In wellbore tubulars, ..... is typically expressed as tension or compression and may result from applied conditions such as set-down-weight, or be induced by operating conditions or variations such as changes in temperature that cause expansion or contraction of components.

stress

The force applied to a body that can result in deformation, or strain, usually described in terms of magnitude per unit of area, or intensity.

hydrostatic pressure

The force per unit area caused by a column of fluid. In US oilfield units, this is calculated using the equation: MW*Depth*0.052, where MW is the drilling fluid density in pounds per gallon, Depth is the true vertical depth or "head" in feet, and 0.052 is a unit conversion factor chosen such that P results in units of pounds per square in

shut in bottomhole pressure (SIBP)

The force per unit area exerted at the bottom of a wellbore when it is closed at either the Christmas tree or the BOP stack. It is generated by a combination of the hydrostatic pressure from the weight of the liquid in the well and any additional applied pressure. The applied pressure component may be from the formation or from an external source at the surface.

hydraulic head

The force per unit area exerted by a column of liquid at a height above a depth (and pressure) of interest. Fluids flow down a hydraulic gradient, from points of higher to lower hydraulic head. The term is sometimes used synonymously with hydrostatic head.

generation

The formation of hydrocarbons from a source rock as bitumen forms from kerogen and accumulates as oil or gas. This depends on three main factors: the presence of organic matter rich enough to yield hydrocarbons, adequate temperature, and sufficient time to bring the source rock to maturity. Pressure and the presence of bacteria and catalysts also affect generation. Generation is a critical phase in the development of a petroleum system.

formation

The fundamental unit of lithostratigraphy. A body of rock that is sufficiently distinctive and continuous that it can be mapped. In stratigraphy, a formation is a body of strata of predominantly one type or combination of types; multiple formations form groups, and subdivisions of formations are members.

gas cap

The gas that accumulates in the upper portions of a reservoir where the pressure, temperature and fluid characteristics are conducive to free gas. The energy provided by the expansion of the '' '' provides the primary drive mechanism for oil recovery in such circumstances

free gas

The gaseous phase present in a reservoir or other contained area. Gas may be found either dissolved in reservoir fluids or as free gas that tends to form a gas cap beneath the top seal on the reservoir trap. Both free gas and dissolved gas play important roles in the reservoir-drive mechanism.

dolomitization

The geochemical process in supratidal sabkha areas where magnesium [Mg] ions from the evaporation of seawater replace calcium [Ca] ions in calcite, forming the mineral dolomite. The volume of dolomite is less than that of calcite, so the replacement of calcite by dolomite in a rock increases the pore space in the rock by 13% and forms an important reservoir rock. Dolomitization can occur during deep burial diagenesis.

uniformitarianism

The geological principle formulated by James Hutton in 1795 and publicized by Charles Lyell in 1830 that geological processes occurring today have occurred similarly in the past, often articulated as, "The present is the key to the past."

structural

The geometry and spatial arrangement of rocks. The structure or deformation can include many mechanisms, such as folding, faulting and fracturing. Structure can usually be interpreted in terms of the deformation of the crust of the Earth as continents and tectonic plates move and collide.

completion

The hardware used to optimize the production of hydrocarbons from the well. A generic term used to describe the assembly of downhole tubulars and equipment required to enable safe and efficient production from an oil or gas well.

jet

The high-velocity fluid stream produced by the nozzles in the bit.

pipe stretch

The increase in length resulting from the combination of forces acting on a string within the wellbore. The principal factors resulting in an increase in string length are the weight of the string itself and the effects of thermal expansion.

deviated drilling OR directional drilling

The intentional deviation of a wellbore from the path it would naturally take. This is accomplished through the use of whipstocks, bottomhole assembly (BHA) configurations, instruments to measure the path of the wellbore in three-dimensional space, data links to communicate measurements taken downhole to the surface, mud motors and special BHA components and drill bits, including rotary steerable systems, and drill bits.

Backwash or Reverse Circulation

The intentional pumping of wellbore fluids down the annulus and back up through the drillpipe. This is the opposite of the normal direction of fluid circulation in a wellbore. This method can bring bottomhole fluids to the surface faster than normal circulation for a given flow rate

effective porosity

The interconnected pore volume or void space in a rock that contributes to fluid flow or permeability in a reservoir. Effective porosity excludes isolated pores and pore volume occupied by water adsorbed on clay minerals or other grains. Total porosity is the total void space in the rock whether or not it contributes to fluid flow. Effective porosity is typically less than total porosity.

gas-oil contact (GOC)

The interface between the gas and oil phases present in a reservoir formation. During the production of a well, the ''' may move, resulting in undesirable production conditions such as a high proportion of gas that may be too much for surface processing facilities. Monitoring the '' '' '' and oil water contacts is a key element of good reservoir management practices.

fluid contact

The interface that separates fluids of different densities in a reservoir. Horizontal contacts are usually assumed, although tilted contacts occur in some reservoirs. The contact between fluids is usually gradual rather than sharp, forming a transition zone of mixed fluid. A mixed-fluid reservoir will stratify according to fluid density, with gas at the top, oil in the middle, and water below. Production of fluids often perturbs the fluid contacts in a reservoir.

contact

The interface, also called fluid contact, that separates fluids of different densities in a reservoir. Horizontal contacts are usually assumed, although tilted contacts occur in some reservoirs. The contact between fluids is usually gradual rather than sharp, forming a transition zone of mixed fluid. A mixed-fluid reservoir will stratify according to fluid density, with gas at the top, oil in the middle, and water below. Production of fluids often perturbs the fluid contacts in a reservoir.

mantle

The intermediate layer of the Earth beneath the crust that is about 2900 km thick [1820 miles] and overlies the core of the Earth. The mantle consists of dense igneous rocks like pyroxenite and dunite, composed of the minerals pyroxene and olivine. The crust, mantle and core of the Earth are distinguished from the lithosphere and asthenosphere on the basis of their composition and not their mechanical behavior. The Mohorovicic discontinuity abruptly separates the crust from the mantle, where the velocity of compressional waves is significantly higher.

flow line OR mud return line

The large-diameter metal pipe that connects the bell nipple under the rotary table to the possum belly at the mud tanks. It is simply an inclined, gravity-flow conduit to direct mud coming out the top of the wellbore to the mud surface-treating equipment.

Gravity drainage

The least common primary recovery mechanism in which the force of gravity pushes hydrocarbons out of the reservoir, into the wellbore and up to surface. Its effect is greater in thick gas-condensate reservoirs and in shallow, highly permeable, steeply dipping reservoirs.

Measured Depth, MD

The length of the wellbore, as if determined by a measuring stick. This measurement differs from the true vertical depth of the well in all but vertical wells.

measured depth (MD)

The length of the wellbore, as if determined by a measuring stick. This measurement differs from the true vertical depth of the well in all but vertical wells. Since the wellbore cannot be physically measured from end to end, the lengths of individual joints of drillpipe, drill collars and other drillstringelements are measured with a steel tape measure and added together.

methane

The lightest and most abundant of the hydrocarbon gases and the principal component of natural gas. Methane is a colorless, odorless gas that is stable under a wide range of pressure and temperature conditions in the absence of other compounds.

mechanical sticking

The limiting or prevention of motion of the drillstring by anything other than differential pressure sticking. It can be caused by junk in the hole, wellbore geometry anomalies, cement, keyseats or a buildup of cuttings in the annulus.

annular velocity

The linear velocity of a fluid passing through an annular space. The term critical '' '' is often used to describe the flow rate or velocity at which entrained solids will be efficiently transported by the annular fluid. If the fluid velocity falls below the critical rate, there will be a risk of particles settling, forming beds or bridges that may obstruct the wellbore.

drilling foreman

The location supervisor for the drilling contractor. He is usually a senior, experienced individual who has worked his way up through the ranks of the drilling crew positions. His job is largely administrative, including ensuring that the rig has sufficient materials, spare parts and skilled personnel to continue efficient operations.

pusher OR drilling foreman OR toolpusher

The location supervisor for the drilling contractor. The toolpusher is usually a senior, experienced individual who has worked his way up through the ranks of the drilling crew positions. His job is largely administrative, including ensuring that the rig has sufficient materials, spare parts and skilled personnel to continue efficient operations.

Casing Point

The location, or depth, at which drilling an interval of a particular diameter hole ceases, so that casing of a given size can be run and cemented

casing point

The location, or depth, at which drilling an interval of a particular diameter hole ceases, so that casing of a given size can be run and cemented.

circulation loss

The loss of drilling fluid to a formation, usually caused when the hydrostatic head pressure of the column of drilling fluid exceeds the formation pressure.

Circulation Loss

The loss of drilling fluid to a formation, usually caused when the hydrostatic head pressure of the column of drilling fluid exceeds the formation pressure. This loss of fluid may be loosely classified as seepage losses, partial losses or catastrophic losses, each of which is handled differently depending on the risk to the rig and personnel and the economics of the drilling fluid and each possible solution.

bottomhole assembly

The lower portion of the drillstring, consisting of (from the bottom up in a vertical well) the bit, bit sub, a mud motor (in certain cases), stabilizers, drill collar, heavy-weight drillpipe, jarring devices ("jars") and crossovers for various threadforms. Must provide force for the bit to break the rock (weight on bit), survive a hostile mechanical environment and provide the driller with directional control of the well.

Bottom Hole Assembly or BHA

The lower portion of the drillstring, consisting of the bit, bit sub, a mud motor, stabilizers, drill collar, heavy-weight drillpipe, jarring devices and crossovers for various threadforms. This assembly must provide force for the bit to break the rock, survive a hostile mechanical environment and provide the driller with directional control of the well.

operating gas-lift valve (OGLV)

The lowermost gas-lift valve in a gas-lift completion through which the lift gas is injected during normalproduction. During startup, the upper gas-lift valves open in sequence, from the top down, to enable the tubing fluids to be displaced.

Bottom dead centre

The lowermost point of the SRP horsehead in a stroke

drawworks

The machine on the rig consisting of a large-diameter steel spool, brakes, a power source and assorted auxiliary devices. The primary function is to reel out and reel in the drilling line, a large diameter wire rope, in a controlled fashion.

rig

The machine used to drill a wellbore.

drilling rig

The machine used to drill a wellbore. In onshore operations, it includes virtually everything except living quarters. Major components include the mud tanks, the mud pumps, the derrick or mast, the drawworks, the rotary table or topdrive, the drillstring, the power generation equipment and auxiliary equipment.

lithology

The macroscopic nature of the mineral content, grain size, texture and color of rocks.

leak off

The magnitude of pressure exerted on a formation that causes fluid to be forced into the formation. The fluid may be flowing into the pore spaces of the rock or into cracks opened and propagated into the formation by the fluid pressure. This term is normally associated with a test to determine the strength of the rock, commonly called a pressure integrity test (PIT) or aleakoff test (LOT).

dip

The magnitude of the inclination of a plane from horizontal. True, or maximum, dip is measured perpendicular to strike. Apparent dip is measured in a direction other than perpendicular to strike.

primary completion components

The main elements of an oil or gas well, including the production tubing string, that enable a particular type or design of completion to function as designed.

passive margin

The margin of a continent and ocean that does not coincide with the boundary of a lithospheric plate and along which collision is not occurring. Passive margins are characterized by rifted, rotated fault blocks of thick sediment, such as the present-day Gulf of Mexico and Atlantic margins of North America.

Solubility

The maximum amount of a substance that will dissolve in a given amount of solvent at a given temperature and pressure, or the degree to which a substance will dissolve in a particular solvent.

primary recovery method

The means by which the initial reservoir production is achieved, such as natural production from a gas-drive reservoir. In many cases, a secondary recovery method, such as waterflood, is required to maintain a viable reservoir production rate.

convergence

The movement of tectonic plates toward each other, generating compressional forces and ultimately resulting in collision, and in some cases subduction, of tectonic plates. The boundary where tectonic plates converge is called a convergent margin.

Buckley-Leverret theory

The name of the theory which provides us with the analytical solution for immiscible displacement

erosion.1

The process of denudation of rocks, including physical, chemical and biological breakdown and transportation.

absolute age

The measurement of age in years. The determination of this of rocks, minerals and fossils, in years before the present, is the basis for the field of geochronology. The measurement of the decay of radioactive isotopes, especially uranium, strontium, rubidium, argon and carbon, has allowed geologists to more precisely determine the age of rock formations. Tree rings and seasonal sedimentary deposits called varves can be counted to determine absolute age. Although the term implies otherwise, "absolute" ages typically have some amount of potential error and are inexact. Relative age, in contrast, is the determination of whether a given material is younger or older than other surrounding material on the basis of stratigraphic and structural relationships, such as superposition, or by interpretation of fossil content.

logging while drilling (LWD)

The measurement of formation properties during the excavation of the hole, or shortly thereafter, through the use of tools integrated into the bottomhole assembly. While sometimes risky and expensive, it has the advantage of measuring properties of a formation before drilling fluids invade deeply.

absolute pressure

The measurement of pressure relative to the pressure in a vacuum, equal to the sum of the pressure shown on a pressure gauge and atmospheric pressure.

absolute permeability

The measurement of the permeability, or ability to flow or transmit fluids through a rock, conducted when a single fluid, or phase, is present in the rock. The symbol most commonly used for permeability is k, which is measured in units of darcies or millidarcies.

Brake

The mechanism on the drawworks that permits the driller to control the speed and motion of the drilling line and the drillstring

motorman

The member of the rig crew responsible for maintenance of the engines. While all members of the rig crew help with major repairs, this member does routine preventive maintenance and minor repairs.

secondary production

The method used to sustain production levels at viable rates following a fall in flow rate as the efficiency of the primary production methods declines. methods frequently involve an artificial-lift system or reservoir injection for pressure maintenance.

sand production

The migration of formation sand caused by the flow of reservoir fluids. The production of sand is generally undesirable since it can restrict productivity, erode completion components, impede wellbore access, interfere with the operation of downhole equipment, and present significant disposal difficulties.

regression

The migration of shoreline into a basin during progradation due to a fall in relative sea level. Deposition during a regression can juxtapose shallow-water sediments atop deep-water sediments.

transgression

The migration of shoreline out of a basin and onto land during retrogradation. A transgression can result in sediments characteristic of shallow water being overlain by deeper water sediments.

Critical saturation

The minimum saturation at which a phase becomes mobile

Mobility ratio

The mobility of an injectant divided by that of the fluid it is displacing, such as oil.

magma

The molten rock in the Earth that can either rise to the surface as lava and form extrusive igneous rock or cool within the Earth to form plutonic igneous rock.

rhombohedral packing

The most compact arrangement in space of uniform spheres (atoms and molecules in mineral crystals, or grains in sedimentary rocks) that results in a structure having no more than 26% porosity. Rhombohedral packing is more stable mechanically than cubic packing. Cubic packing is the most porous packing arrangement, with about 47% porosity in the ideal situation. Most sediments, however, are not uniform spheres of the same size, nor can they be arranged in a cubic structure naturally, so most sediments have much less than 47% porosity of ideal cubic packing and commonly less than the 26% porosity of ideal rhombohedral packing.

Micellar-Polymer flooding or surfactant flooding

The most predominant EOR technique used for achieving low Interfacial tension is _________

midoceanic ridge

The mountainous, linear axis of ocean basins along which rifting occurs and new oceanic crust forms as magma wells up and solidifies. The most prominent midoceanic ridges are those of the Atlantic and Indian Oceans. The new crust is made of mafic igneous rock called basalt, commonly referred to as midocean ridge basalt, or MORB, whose composition reflects that of the deeper mantle of the Earth. The presence of the spreading plate boundaries of the midoceanic ridges; their symmetrically spreading, successively older crust outward from the ridge; and the lack of oceanic crust older than approximately 200 Ma support the theory of plate tectonics and the recycling of oceanic crust through the process of subduction.

fines migration

The movement of fine clay, quartz particles or similar materials within the reservoir formation due to drag forces during production. ''' ''' may result from an unconsolidated or inherently unstable formation, or from use of an incompatible treatment fluid that liberates fine particles. Unlike sandmigration that is best stabilized, the material mobilized in '' ''' should be produced to avoid near-wellbore damage.

secondary migration

The movement of generated hydrocarbons into a reservoir after their expulsion, or primary migration, from a source rock.

migration

The movement of hydrocarbons from their source into reservoir rocks. The movement of newly generated hydrocarbons out of their source rock is primary migration, also called expulsion. The further movement of the hydrocarbons into reservoir rock in a hydrocarbon trap or other area of accumulation is secondary migration. Migration typically occurs from a structurally low area to a higher area because of the relative buoyancy of hydrocarbons in comparison to the surrounding rock. Migration can be local or can occur along distances of hundreds of kilometers in large sedimentary basins, and is critical to the formation of a viable petroleum system.

kerogen

The naturally occurring, solid, insoluble organic matter that occurs in source rocks and can yield oil upon heating. This is the portion of naturally occurring organic matter that is nonextractable using organic solvents. Typical organic constituents of kerogen are algae and woody plant material. Kerogens have a high molecular weight relative to bitumen, or soluble organic matter. Bitumen forms from kerogen during petroleum generation. Kerogens are described as Type I, consisting of mainly algal and amorphous (but presumably algal) kerogen and highly likely to generate oil; Type II, mixed terrestrial and marine source material that can generate waxy oil; and Type III, woody terrestrial source material that typically generates gas.

hydrostatic pressure

The normal, predicted pressure for a given depth, or the pressure exerted per unit area by a column of freshwater from sea level to a given depth. Abnormally low pressure might occur in areas where fluids have been drained, such as a depleted hydrocarbon reservoir. Abnormally high pressure might occur in areas where burial of water-filled sediments by an impermeable sediment such as clay was so rapid that fluids could not escape and the pore pressure increased with deeper burial.

virgin pressure

The original, undisturbed pressure of a reservoir prior to fluid production.

Bit Nozzle

The part of the bit that includes a hole or opening for drilling fluid to exit. The hole is usually small and the pressure of the fluid inside the bit is usually high, leading to a high exit velocity

Injection pattern

The particular arrangement of production and injection wells. For an individual field or part of a field this is based on the location of existing wells, reservoir size and shape, cost of new wells and the recovery increase associated with various arrangements. Examples include the line drive, staggered line drive, two-spot, three-spot, four-spot, five-spot, seven-spot and nine-spot.

porosity

The percentage of pore volume or void space, or that volume within rock that can contain fluids. Porosity can be a relic of deposition (primary porosity, such as space between grains that were not compacted together completely) or can develop through alteration of the rock (secondary porosity, such as when feldspar grains or fossils are preferentially dissolved from sandstones). Porosity can be generated by the development of fractures, in which case it is called fracture porosity. Effective porosity is the interconnected pore volume in a rock that contributes to fluid flow in a reservoir. It excludes isolated pores. Total porosity is the total void space in the rock whether or not it contributes to fluid flow. Thus, effective porosity is typically less than total porosity. Shale gas reservoirs tend to have relatively high porosity, but the alignment of platy grains such as clays makes their permeability very low.

life of the well

The period of time during which economically sustainable production levels may be expected from a well. The anticipated ''' ''' and the characteristics of the reservoir fluid are the two main factors in specifying the completion system components.

Magnetic Reversal Sequence (MRS)

The periodic switching of the magnetic north and south poles of the Earth throughout time, probably as a result of movement of fluid within the Earth's core. The onset and duration of the many episodes of reversed polarity have been documented by examining the polarity of magnetic minerals within rocks of different ages from around the world, particularly in basalts or igneous rocks of the oceanic crust. Oceanic basalts record the Earth's magnetic field as they solidify from molten lava symmetrically on each side of the midoceanic ridges. These data have been compiled to create a time scale known as the geomagnetic polarity time scale (GPTS). In the oil field, borehole recordings allow direct correlation to GPTS and well-to-well correlations.

geomagnetic polarity reversal

The periodic switching of the magnetic north and south poles of the Earth throughout time, probably as a result of movement of fluid within the Earth's core. The onset and duration of the many episodes of reversed polarity have been documented by examining the polarity of magnetic minerals within rocks of different ages from around the world, particularly in basalts or igneous rocks of the oceanic crust. Oceanic basalts record the Earth's magnetic field as they solidify from molten lava symmetrically on each side of the midoceanic ridges. These data have been compiled to create a time scale known as the geomagnetic polarity time scale (GPTS). In the oil field, borehole recordings allow direct correlation to GPTS and well-to-well correlations.

strain

The permanent deformation evident in rocks and other solid bodies that have experienced a sufficiently high applied stress. A change in shape, such as folding, faulting, fracturing, or change, generally a reduction, in volume are common examples of strain seen in rocks. Strain can be described in terms of normal and shear components, and is the ratio of the change in length or volume to the initial length or volume. For more on strain: Means WD: Stress and Strain. New York, New York, Springer-Verlag, 1976.

accumulation

The phase in the development of a petroleum system during which hydrocarbons migrate into and remain trapped in a reservoir.

preservation

The phase of a petroleum system after hydrocarbons accumulate in a trap and are subject to degradation, remigration, tectonism or other unfavorable or destructive processes.

appraisal

The phase of petroleum operations that immediately follows successful exploratory drilling. During this, delineation wells might be drilled to determine the size of the oil or gas field and how to develop it most efficiently.

nipple-down

The process of disassembling well-control or pressure-control equipment on the wellhead.

development

The phase of petroleum operations that occurs after exploration has proven successful, and before full-scale production. The newly discovered oil or gas field is assessed during an appraisal phase, a plan to fully and efficiently exploit it is created, and additional wells are usually drilled.

production

The phase that occurs after successful exploration and development and during which hydrocarbons are drained from an oil or gas field.

catagenesis

The physical and chemical alteration of sediments and pore fluids at temperatures and pressures higher than those of diagenesis. Catagenesis involves heating in the range of 50° to 150°C [122° to 302°F]. At these temperatures, chemical bonds break down in kerogen and clays within shale, generating liquid hydrocarbons. At the high end of this temperature range, secondary cracking of oil molecules can generate gas molecules.

sandface

The physical interface between the formation and the wellbore. The diameter of the wellbore at the sandface is one of the dimensions used in production models to assess potential productivity.

compaction

The physical process by which sediments are consolidated, resulting in the reduction of pore space as grains are packed closer together. As layers of sediment accumulate, the ever increasing overburden pressure during burial causes compaction of the sediments, loss of pore fluids and formation of rock as grains are welded or cemented together.

weathering

The physical, chemical and biological processes that decompose rock at and below the surface of the Earth through low pressures and temperatures and the presence of air and water. Weathering includes processes such as dissolution, chemical weathering, disintegration and hydration.

diagenesis

The physical, chemical or biological alteration of sediments into sedimentary rock at relatively low temperatures and pressures that can result in changes to the rock's original mineralogy and texture. After deposition, sediments are compacted as they are buried beneath successive layers of sediment and cemented by minerals that precipitate from solution. Grains of sediment, rock fragments and fossils can be replaced by other minerals during diagenesis. Porosity usually decreases during diagenesis, except in rare cases such as dissolution of minerals and dolomitization. Diagenesis does not include weathering processes. Hydrocarbon generation begins during diagenesis. There is not a clear, accepted distinction between diagenesis and metamorphism, although metamorphism occurs at pressures and temperatures higher than those of the outer crust, where diagenesis occurs.

neutral point

The point on a string of tubulars at which there are neither tension nor compression forces present.

holdup depth

The point or depth at which a tool or drift of a specific size can no longer pass through the wellbore. A higher than expected '' '' may result from scale, fill, distortion of the wellbore tubulars orformation movement in an openhole completion.

HUD

The point or depth at which a tool or drift of a specific size can no longer pass through the wellbore. A higher than expected ''' ''' may result from scale, fill, distortion of the wellbore tubulars orformation movement in an openhole completion.

Pore volumes

The popular units used for measuring the volume of the displacement fluid

normal pressure. Ask what is pressure gradient for freshwater and for water with dissolved solids

The pore pressure of rocks that is considered normal in areas in which the change in pressure per unit of depth is equivalent to hydrostatic pressure. The normal hydrostatic pressure gradient for freshwater is 0.433 pounds per square inch per foot (psi/ft), or 9.792 kilopascals per meter (kPa/m), and 0.465 psi/ft for water with 100,000 ppm total dissolved solids (a typical Gulf Coast water), or 10.516 kPa/m.

secondary porosity

The porosity created through alteration of rock, commonly by processes such as dolomitization, dissolution and fracturing.

primary porosity

The porosity preserved from deposition through lithification.

production wing

The portion of a Christmas tree or surface production facility through which production fluids flow.

Oil bank

The portion of a reservoir where the oil saturation is increased because of the application of an improved oil recovery method.

stuck pipe

The portion of the drillstring that cannot be rotated or moved vertically.

formation pressure

The pressure of fluids within the pores of a reservoir, usually hydrostatic pressure, or the pressure exerted by a column of water from the formation's depth to sea level. When impermeable rocks such as shales form as sediments are compacted, their pore fluids cannot always escape and must then support the total overlying rock column, leading to anomalously high formation pressures. Because reservoir pressure changes as fluids are produced from a reservoir, the pressure should be described as measured at a specific time, such as initial reservoir pressure.

sieve analysis

The process of analyzing the size distribution of a sand or gravel sample. In sand-control applications, a sample of formation sand is shaken through a series of sieves of known size. The resulting distribution is then used to design an appropriate treatment that will retain the sand, while causing a minimal restriction to production.

flange up

The process of assembling flanged components such as pressure-control equipment.

pore pressure

The pressure of fluids within the pores of a reservoir, usually hydrostatic pressure, or the pressure exerted by a column of water from the formation's depth to sea level. When impermeable rocks such as shales form as sediments are compacted, their pore fluids cannot always escape and must then support the total overlying rock column, leading to anomalously high formation pressures. Because reservoir pressure changes as fluids are produced from a reservoir, the pressure should be described as measured at a specific time, such as initial reservoir pressure.

reservoir pressure

The pressure of fluids within the pores of a reservoir, usually hydrostatic pressure, or the pressure exerted by a column of water from the formation's depth to sea level. When impermeable rocks such as shales form as sediments are compacted, their pore fluids cannot always escape and must then support the total overlying rock column, leading to anomalously high formation pressures. Because reservoir pressure changes as fluids are produced from a reservoir, the pressure should be described as measured at a specific time, such as initial reservoir pressure.

formation pressure

The pressure of the subsurface formation fluids, commonly expressed as the density of fluid required in the wellbore to balance that pore pressure.

reservoir pressure

The pressure of the subsurface formation fluids, commonly expressed as the density of fluid required in the wellbore to balance that pore pressure.

lithostatic pressure

The pressure of the weight of overburden, or overlying rock, on a formation; also called geostatic pressure.

geostatic pressure

The pressure of the weight of overburden, or overlying rock, on a formation; also called lithostatic pressure.

fracture gradient

The pressure required to induce fractures in rock at a given depth.

back pressure

The pressure within a system caused by fluid friction or an induced resistance to flow through the system. Most process facilities require a minimum system pressure to operate efficiently. The necessary '' '' is often created and controlled by a valve that is set to operate under the desired range of conditions.

back-pressure

The pressure within a system caused by fluid friction or an induced resistance to flow through the system. Most process facilities require a minimum system pressure to operate efficiently. The necessary back-pressure is often created and controlled by a valve that is set to operate under the desired range of conditions.

geopressure

The pressure within the Earth, or formation pressure. The common oilfield usage, however, is to indicate anomalous subsurface pore pressure that is higher or lower than the normal, predicted hydrostatic pressure for a given depth, or the pressure exerted per unit area by a column of fresh water from sea level to a given depth. Abnormally low pore pressure might occur in areas where fluids have been drained, such as a depleted hydrocarbon reservoir. Abnormally high pore pressure might occur in areas where burial of water-filled sediments by an impermeable sediment such as clay was so rapid that fluids could not escape and the pore pressure increased with deeper burial.

reservoir pressure

The pressure within the reservoir rock.

formation pressure

The pressure within the reservoir rock. The '' ''' value can be further categorized as relating to flowing well or shut-in conditions.

pore pressure

The pressure within the reservoir rock. The formation pressure value can be further categorized as relating to flowing well or shut-in conditions.

Bottom Hole Pressure or BHP

The pressure, usually measured in pounds per square inch (psi), at the bottom of the hole. This pressure may be calculated in a static, fluid-filled wellbore with the equation: P = MW * Depth * 0.052

shaker OR shale shaker

The primary and probably most important device on the rig for removing drilled solids from the mud.

production string

The primary conduit through which reservoir fluids are produced to surface. The ''' ''' is typically assembled with tubing and completion components in a configuration that suits the wellbore conditions and the production method. An important function of the '' ''' is to protect the primary wellbore tubulars, including the casing and liner, from corrosion or erosion by the reservoir fluid.

Compressor

The prime mover in a Gas lift system

depth control

The procedures and equipment used to measure and correlate depth to ensure that a treatment is applied at the correct position within the wellbore.

erosion.2

The process by which material weathered from rocks is transported by wind, water, ice, or abrasive solid particles, or by mass-wasting, as in rock falls and landslides.

metamorphism

The process by which the characteristics of rocks are altered or the rock is recrystallized. Metamorphism of igneous, sedimentary, or preexisting metamorphic rock can produce new metamorphic rock. Such alteration occurs as rocks respond to changes in temperatures, pressures and fluids, commonly along the edges of colliding lithospheric plates. The pressures and temperatures at which metamorphism occurs are higher than those of diagenesis, but no clear boundary between the two has been established.

lithification

The process by which unconsolidated sediments become sedimentary rock. Sediments typically are derived from preexisting rocks by weathering, transported and redeposited, and then buried and compacted by overlying sediments. Cementation causes the sediments to harden, or lithify, into rock.

hot tapping

The process of drilling a hole through a pressure barrier using special equipment and procedures to ensure that the pressure and fluids are safely contained when access is made. This process is often used to enable access to the wellbore when wellhead valves jam closed.

primary cementing

The process of placing a cement sheath around a casing or liner string. The main objectives of '' ''' operations include zonal isolation to prevent migration of fluids in the annulus, support for the casing or liner string, and protection of the casing string from corrosive formation fluids.

Bit Trip

The process of pulling the drillstring out of the wellbore for the purpose of changing a worn or underperforming drill bit.

embrittlement

The process whereby steel components become less resistant to breakage and generally much weaker in tensile strength.

Hydrogen embrittlement

The process whereby steel components become less resistant to breakage and generally much weaker in tensile strength. On a molecular level, hydrogen ions work their way between the grain boundaries of the steel, where hydrogen ions recombine into molecular hydrogen [H2], taking up more space and weakening the bonds between the grains. The formation of molecular hydrogen can cause sudden metal failure due to cracking when the metal is subjected to tensile stress.

acidizing

The pumping of acid into the wellbore to remove near-well formation damage and other damaging substances. This procedure commonly enhances production by increasing the effective well radius. When performed at pressures above the pressure required to fracture the formation, the procedure is often referred to as acid fracturing.

gas prone

The quality of a source rock that makes it more likely to generate gas than oil. The nature of the organic matter or kerogen in source rocks varies from coaly, plant-like material commonly found in terrestrial source rocks to algal or other marine material that makes up marine source rocks. Terrestrial source rocks are commonly gas-prone.

oil-prone

The quality of a source rock that makes it more likely to generate oil than gas. The nature of the organic matter (kerogen) in source rocks varies from coaly, plant-like material commonly found in terrestrial source rocks to algal or other marine material that makes up marine source rocks. Marine source rocks are commonly oil-prone.

homogeneity

The quality of uniformity of a material. If irregularities are distributed evenly in a mixture of material, the material is homogeneous. (Compare with heterogeneity.)

heterogeneity

The quality of variation in rock properties with location in a reservoir or formation. Shale gas reservoirs are heterogeneous formations whose mineralogy, organic content, natural fractures, and other properties vary from place to place. This heterogeneity makes petroleum system modeling, formation evaluation, and reservoir simulation critical to maximizing production from shale reservoirs.

sorting

The range of sedimentary grain sizes that occurs in sediment or sedimentary rock. The term also refers to the process by which sediments of similar size are naturally segregated during transport and deposition according to the velocity and transporting medium. Well-sorted sediments are of similar size (such as desert sand), while poorly-sorted sediments have a wide range of grain sizes (as in a glacial till). A well-sorted sandstone tends to have greater porosity than a poorly sorted sandstone because of the lack of grains small enough to fill its pores. Conglomerates tend to be poorly sorted rocks, with particles ranging from boulder size to clay size.

geothermal gradient

The rate of increase in temperature per unit depth in the Earth. Although this varies from place to place, it averages 25 to 30 °C/km [15 °F/1000 ft]. Temperature gradients sometimes increase dramatically around volcanic areas. It is particularly important for drilling fluids engineers to know the geothermal gradient in an area when they are designing a deep well. The downhole temperature can be calculated by adding the surface temperature to the product of the depth and the geothermal gradient.

volumetric efficiency

The ratio of the actual output volume of a positive displacement pump divided by the theoretical geometric maximum volume of liquid that the pump could output under perfect conditions. Inefficiencies are caused by gaseous components (air and methane) being trapped in the liquid mud, leaking and noninstantaneously sealing valves in the pumps, fluid bypass of pump swab seals, and mechanical clearances and "play" in various bearings and connecting rods in the pumps. This efficiency is usually expressed as a percentage, and ranges from about 92% to 99% for most modern rig pumps and cement pumps. For critical calculations, this efficiency can be determined by a rigsite version of the "bucket and stopwatch" technique, whereby the rig crew will count the number of pump strokes required to pump a known volume of fluid. In cementing operations, displacement is often measured by alternating between two 10-bbl displacement tanks.

subsidence

The relative sinking of the Earth's surface. Plate tectonic activity (particularly extension of the crust, which promotes thinning and sinking), sediment loading and removal of fluid from reservoirs are processes by which the crust can be depressed. Subsidence can produce areas in which sediments accumulate and, ultimately, form sedimentary basins.

asthenosphere

The relatively plastic layer of the upper mantle of the Earth on which the tectonic plates of the lithosphere move. The asthenosphere is approximately 200 km [124 miles] thick and, owing to its depth below the Earth's surface, warm (~ 1400 oC) [2640 oF] but not molten. Here the mantle deforms by plastic flow in response to applied pressures above 100 MPa [14,500 psi]. This zone is considered coincidental, at least below oceanic crust, with the low-velocity zone of the upper mantle.

derrick floor OR rig floor

The relatively small work area in which the rig crew conducts operations, usually adding or removing drillpipe to or from the drillstring. It is the most dangerous location on the rig because heavy iron is moved around there. Drillstring connections are made or broken on the this location, and the driller's console for controlling the major components of the rig are located there.

workover

The repair or stimulation of an existing production well for the purpose of restoring, prolonging or enhancing the production of hydrocarbons.

company man OR company representative

The representative of the oil company or operator on a drilling location. For land operations, he/she is responsible for operational issues on the location, including the safety and efficiency of the project.

inversion

The reversal of features, particularly structural features such as faults, by reactivation. For example, a normal fault might move in a direction opposite to its initial movement.

rotary table

The revolving or spinning section of the drillfloor that provides power to turn the drillstring in a clockwise direction (as viewed from above). The rotary motion and power are transmitted through the kelly bushing and the kelly to the drillstring.

basement

The rock layer below which economic hydrocarbon reservoirs are not expected to be found, sometimes preceded by economic. This is usually older, deformed igneous or metamorphic rocks, which seldom develops the porosity and permeability necessary to serve as a hydrocarbon reservoir, and below which sedimentary rocks are not common. Basement rocks typically have different density, acoustic velocity, and magnetic properties from overlying rocks.

Pitman arm

The rod connecting the Crank of the Gearbox to the Walking beam in an SRP assembly

crushed zone

The rubblized or damaged zone surrounding a perforation tunnel where the action of the perforating charge or bullet has altered the formation structure and permeability. Although it is generally damaging to production, the severity or extent of the ''' depend greatly on the characteristics of the formation, the perforating charge and the underbalance or overbalance conditions at time of perforating. Measures to reduce the effect of the crushed zone include underbalanced perforating in which the crushed zone and perforating debris are flushed from the perforating tunnel by the reservoir fluid as soon as the perforation is created. Where overbalanced perforating techniques are used, it may be necessary to acidize the ''' to achieve maximum productivity from the perforated interval.

crushed zone

The rubblized rock just below the tooth of a rock bit.

crushed zone

The rubblized rock just below the tooth of a rock bit. Rock in this zone fails due to the high compressive stress placed on it by the bit tooth (in the case of a roller-cone bit).

Residual saturation or irreducible saturation

The saturation of a phase present after explusion of the entire non-wetting phase

Water wet

The scenario whereby a thin film of water coats the surface of the formation matrix, a condition that is desirable for efficient oil transport.

Secondary recovery

The second stage of hydrocarbon production during which an external fluid such as water or gas is injected into the reservoir through injection wells located in rock that has fluid communication with production wells.

travelling block

The set of sheaves that move up and down in the derrick.

Christmas tree

The set of valves, spools and fittings connected to the top of a well to direct and control the flow offormation fluids from the well.

Annular Velocity

The speed at which drilling fluid or cement moves in the annulus. It is important to monitor this speed to ensure that the hole is being properly cleaned of cuttings, cavings and other debris while avoiding erosion of the borehole wall.

penetration rate

The speed at which the drill bit can break the rock under it and thus deepen the wellbore. This speed is usually reported in units of feet per hour or meters per hour.

exit velocity

The speed the drilling fluid attains when accelerated through bit nozzles, typically in the low-hundreds of feet per second.

maturity

The state of a source rock with respect to its ability to generate oil or gas. As a source rock begins to mature, it generates gas. As an oil-prone source rock matures, the generation of heavy oils is succeeded by medium and light oils. Above a temperature of approximately 100 oC [212 oF], only dry gas is generated, and incipient metamorphism is imminent. The maturity of a source rock reflects the ambient pressure and temperature as well as the duration of conditions favorable for hydrocarbon generation.

isostasy

The state of gravitational equilibrium between the lithosphere and the asthenosphere of the Earth such that lithospheric plates "float" at a given elevation depending on their thickness. The balance between the elevation of the lithospheric plates and the asthenosphere is achieved by the flowage of the denser asthenosphere. Various hypotheses about isostasy take into account density (Pratt hypothesis), thickness (Airy hypothesis), and pressure variations to explain topographic variations among lithospheric plates. The current model consists of several layers of different density.

dynamic positioning

The stationing of a vessel, especially a drillship or semisubmersible drilling rig, at a specific location in the sea by the use of computer-controlled propulsion units called thrusters.

dog house

The steel-sided room adjacent to the rig floor, usually having an access door close to the driller's controls. This general-purpose shelter is a combination tool shed, office, communications center, coffee room, lunchroom and general meeting place for the driller and his crew.

superposition

The stratigraphic principle that, in the case of undeformed, flat-lying strata, younger layers are deposited atop older ones, such that the top layer is youngest and underlying layers increase in age with depth. Nicolaus Steno articulated the law of superposition of strata in the 17th century.

spill point

The structurally lowest point in a hydrocarbon trap that can retain hydrocarbons. Once a trap has been filled to its spill point, further storage or retention of hydrocarbons will not occur for lack of reservoir space within that trap. The hydrocarbons spill or leak out, and they continue to migrate until they are trapped elsewhere.

mast

The structure used to support the crown block and the drillstring. They are usually rectangular or trapezoidal in shape and offer a very good stiffness, important to land rigs whose said structure is laid down when the rig is moved. They suffer from being heavier than conventional derricks and consequently are not usually found in offshore environments, where weight is more of a concern than in land operations.

derrick

The structure used to support the crown blocks and the drillstring of a drilling rig. It is usually pyramidal in shape, and offer a good strength-to-weight ratio.

lithostratigraphy

The study and correlation of strata to elucidate Earth history on the basis of their lithology, or the nature of the well log response, mineral content, grain size, texture and color of rocks.

Sandstone petrography

The study of and description of sandstones, including the mineral content.

palynology

The study of fossilized remnants of microscopic entities having organic walls, such as pollen, spores and cysts from algae. Changes in the Earth through time can be documented by studying the distribution of spores and pollen. Well log and other correlations are enhanced by incorporating palynology. Palynology also has utility in forensics.

paleontology

The study of fossilized, or preserved, remnants of plant and animal life. Changes in the Earth through time can be documented by observing changes in the fossils in successive strata and the environments in which they formed or were preserved. Fossils can also be compared with their extant relatives to assess evolutionary changes. Correlations of strata can be aided by studying their fossil content, a discipline called biostratigraphy.

micropaleontology

The study of microfossils too small to be seen without the use of a microscope. Marine microfossils such as foraminifera are important for stratigraphic correlation.

geologic

The study of the Earth-its history, structure, composition, life forms and the processes that continue to change it.

geology

The study of the Earth-its history, structure, composition, life forms and the processes that continue to change it.

chronostratigraphy

The study of the ages of strata. The comparison, or correlation, of separated strata can include study of their relative or absolute ages.

geochemistry

The study of the chemistry of the Earth and within solid bodies of the solar system, including the distribution, circulation and abundance of elements (and their ions and isotopes), molecules, minerals, rocks and fluids. For geochemists in the petroleum industry, source rock geochemistry is a major focus. Geochemical techniques can determine whether a given source rock is rich enough in organic matter to generate hydrocarbons, whether the source rock has generated hydrocarbons, and whether a particular oil sample was generated by a given source rock.

stratigraphy

The study of the history, composition, relative ages and distribution of strata, and the interpretation of strata to elucidate Earth history. The comparison, or correlation, of separated strata can include study of their lithology, fossil content, and relative or absolute age, or lithostratigraphy, biostratigraphy, and chronostratigraphy.

nipple up

To put together, connect parts and plumbing, or otherwise make ready for use. This term is usually reserved for the installation of a blowout preventer stack.

geochronology

The study of the relative or absolute age of rocks, minerals and fossils. Absolute age is the measurement of age in years, but "absolute" ages typically have some amount of error and are inexact. Relative age, in contrast, is the approximate age of rocks, fossils or minerals made by determining the age of the material relative to other surrounding material.

casing hanger

The subassembly of a wellhead that supports the casing string when it is runinto the wellbore. The ''' provides a means of ensuring that the string is correctly located and generally incorporates a sealing device or system to isolate the casing annulus from upper wellhead components.

earthquake

The sudden release of accumulated stress in the Earth by movement or shaking. Earthquakes are caused by tectonic activity, volcanoes and human activity (such as explosions). Earthquakes occur in the outer 720 km [445 miles] of the Earth, where rocks tend to break rather than flow under stress. The magnitude of earthquakes is determined according to the logarithmic Richter scale. An earthquake of magnitude 4.5 can cause damage, although humans can feel earthquakes as weak as magnitude 2.0. The San Francisco earthquake of 1906 measured 8.25 on the Richter scale, and the largest ever recorded were 8.9 magnitude earthquakes in Colombia and Ecuador (1906) and Japan (1933), and 9.5 in Chile (1960).

shut-in pressure (SIP)

The surface force per unit area exerted at the top of a wellbore when it is closed at either the Christmas tree or the BOP stack.

aerated layer

The surface or near-surface, unconsolidated sedimentary layer that has been subject to weathering and whose pores are air-filled instead of liquid-filled. An aerated layer typically has a low seismic velocity.

wellhead

The surface termination of a wellbore that incorporates facilities for installing casing hangers during the well construction phase. This device also incorporates a means of hanging the production tubing and installing the Christmas tree and surface flow-control facilities in preparation for the production phase of the well.

lithologic contact

The surface that separates rock bodies of different lithologies, or rock types. A contact can be conformable or unconformable depending upon the types of rock, their relative ages and their attitudes. A fault surface can also serve as a contact.

wellhead

The system of spools, valves and assorted adapters that provide pressure control of a production well.

well control

The technology focused on maintaining pressure on open formations (that is, exposed to the wellbore) to prevent or direct the flow of formation fluids into the wellbore.

ambient temperature

The temperature at a point or area expressed as an average of the surrounding areas or materials.Generally given to be 70 to 80oF [21 to 27oC]-an average of daily and seasonal variations.

crystallization temperature

The temperature at which crystals will appear in a brine solution of a given density as it cools. In preparing oilfield brines, the ''' can be used to indicate the maximum saturation(density) achievable for a brine solution at a given temperature.

Bottomhole Circulating Temperature (BHCT)

The temperature of the circulating fluid (air, mud, cement or water) at the bottom of the wellbore after several hours of circulation. This temperature is lower than the bottomhole static temperature.

Bottomhole Static Temperature or BHST

The temperature of the undisturbed formation at the final depth in a well. The formation cools during drilling and most of the cooling dissipates after about 24 hours of static conditions, although it is theoretically impossible for the temperature to return to undisturbed conditions. This temperature is measured under static conditions after sufficient time has elapsed to negate any effects from circulating fluids

bottomhole static temperature

The temperature of the undisturbed formation at the final depth in a well. The formation cools during drilling and most of the cooling dissipates after about 24 hours of static conditions, although it is theoretically impossible for the temperature to return to undisturbed conditions. This temperature is measured under static conditions after sufficient time has elapsed to negate any effects from circulating fluids. Tables, charts and computer routines are used to predict '''' as functions of depth, geographic area and various time functions. The '''' is generally higher than the bottomhole circulating temperature, and can be an important factor when using temperature-sensitive tools or treatments.

down lap

The termination of more steeply dipping overlying strata against a surface or underlying strata that have lower apparent dips; a term used to describe a particular geometry of reflections in seismic data in sequence stratigraphy.

downlap

The termination of more steeply dipping overlying strata against a surface or underlying strata that have lower apparent dips; a term used to describe a particular geometry of reflections in seismic data in sequence stratigraphy.

onlap

The termination of shallowly dipping, younger strata against more steeply dipping, older strata, or the termination of low-angle reflections in seismic data against steeper reflections. Onlap is a particular pattern of reflections in seismic data that, according to principles of sequence stratigraphy, occurs during periods of transgression.

casing burst pressure

The theoretical internal pressure differential at which a joint of casing will fail. The ''' value is a key consideration in many well-control and contingency operations and is a major factor in the well design process.

true stratigraphic thickness

The thickness of a bed or rock body after correcting for the dip of the bed or body and the deviation of the well that penetrates it. The values of true stratigraphic thickness in an area can be plotted and contours drawn to create an isopach map.

true vertical thickness

The thickness of a bed or rock body measured vertically at a point. The values of true vertical thickness in an area can be plotted and contours drawn to create an isochore map.

bed thickness

The thickness of a layer or stratum of sedimentary rock measured perpendicular to its lateral extent, presuming deposition on a horizontal surface. Because sediment deposition can occur on inclined surfaces, apparent or measured bed thickness might differ from true bed thickness. The thickness of a given bed often varies along its extent.

crust

The thin, outermost shell of the Earth that is typically 5 km to 75 km thick [3 to 46 miles]. The continental crust comprises rocks similar in composition to granite and basalt (i.e., quartz, feldspar, biotite, amphibole and pyroxene) whereas the composition of oceanic crust is basaltic (pyroxene and feldspar). The crust overlies the more dense rock of the mantle, which consists of rocks composed of minerals like pyroxene and olivine, and the iron and nickel core of the Earth. The Mohorovicic discontinuity abruptly separates the crust from the mantle; the velocity of compressional waves is significantly higher below the discontinuity. The crust, mantle and core of the Earth are distinguished from the lithosphere and asthenosphere on the basis of their composition and not their mechanical behavior.

casing collar

The threaded collar used to connect two joints of casing. The resultingconnection must provide adequate mechanical strength to enable the casing string to be run and cemented in place

tubing thread

The threaded connection used to assemble the tubing string from individual tubing joints.

critical moment

The time of maximum depth of burial of a hydrocarbon source rock. This is the time of highest probability of entrapment and preservation of hydrocarbons in a petroleum system-after traps form and hydrocarbons migrate into a reservoir and accumulate-and marks the beginning of preservation in a viable petroleum system.

hook load

The total force pulling down on the hook. This total force includes the weight of the drillstring in air, the drill collars and any ancillary equipment, reduced by any force that tends to reduce that weight.

matrix acidizing

The treatment of a reservoir formation with a stimulation fluid containing a reactive acid. In sandstoneformations, the acid reacts with the soluble substances in the formation matrix to enlarge the porespaces. In carbonate formations, the acid dissolves the entire formation matrix.

acid job

The treatment of a reservoir formation with a stimulation fluid containing a reactive acid. In sandstoneformations, the acid reacts with the soluble substances in the formation matrix to enlarge the porespaces. In carbonate formations, the acid dissolves the entire formation matrix. In each case, the matrix acidizing treatment improves the formation permeability to enable enhanced production of reservoir fluids.

acid stimulation

The treatment of a reservoir formation with a stimulation fluid containing a reactive acid. In sandstoneformations, the acid reacts with the soluble substances in the formation matrix to enlarge the porespaces. In carbonate formations, the acid dissolves the entire formation matrix. In each case, the matrix acidizing treatment improves the formation permeability to enable enhanced production of reservoir fluids. Matrix acidizing operations are ideally performed at high rate, but at treatment pressures below the fracture pressure of the formation. This enables the acid to penetrate the formation and extend the depth of treatment while avoiding damage to the reservoir formation.

fairway

The trend along which a particular geological feature is likely, such as a sand fairway or a hydrocarbon fairway. Prediction of conceptual fairways helps explorationists develop prospects. Along a sand fairway, for example, sand was transported and, presumably, was deposited, allowing an interpretation of the presence of reservoir rock in the fairway.

tail pipe

The tubulars and completion components run below a production packer. This device may be included in a completion design for several reasons. It can provide a facility for plugs and other temporary flow-control devices, improve downhole hydraulic characteristics, and provide a suspension point for downhole gauges and monitoring equipment.

open hole

The uncased portion of a well.

sediment

The unconsolidated grains of minerals, organic matter or preexisting rocks, that can be transported by water, ice or wind, and deposited. The processes by which sediment forms and is transported occur at or near the surface of the Earth and at relatively low pressures and temperatures. Sedimentary rocks form from the accumulation and lithification of sediment. Sediments are classified according to size by the Udden-Wentworth scale.

underground blowout

The uncontrolled flow of reservoir fluids from one reservoir into the wellbore, along the wellbore, and into another reservoir. This crossflow from one zone to another can occur when a high-pressure zone is encountered, the well flows, and the drilling crew reacts properly and closes the blowout preventers (BOPs). Pressure in the annulus then builds up to the point at which a weak zone fractures. Depending on the pressure at which the fracturing occurs, the flowing formation can continue to flow and losses continue to occur in the fractured zone. Underground blowouts are historically the most expensive problem in the drilling arena, eclipsing the costs of even surface blowouts. It may prove necessary to drill a second kill well in order to remedy an underground blowout.

daylight tour

The work shift of a drilling crew that commences at about the sunrise hour. Drilling operations usually take place around the clock because of the cost to rent a rig. As a result, there are usually two separate crews working twelve-hour tours to keep the operation going.

plate tectonics

The unifying geologic theory developed to explain observations that interactions of the brittle plates of the lithosphere with each other and with the softer underlying asthenosphere result in large-scale changes in the Earth. The theory of plate tectonics initially stemmed from observations of the shapes of the continents, particularly South America and Africa, which fit together like pieces in a jigsaw puzzle and have similar rocks and fossils despite being separated by a modern ocean. As lithospheric plates heat up or cool down depending on their position, or their tectonic environment, relative to each other and to warmer areas deeper within the Earth, they become relatively more or less dense than the asthenosphere and thus tend to rise as molten magma or sink in cold, brittle slabs or slide past each other. Mountain belts can form during plate collisions or an orogeny; diverging plates or rifts can create new midoceanic ridges; plates that slide past one another create transform fault zones (such as the San Andreas fault); and zones of subduction occur where one lithospheric plate moves beneath another. Plate tectonic theory can explain such phenomena as earthquakes, volcanic or other igneous activity, midoceanic ridges and the relative youth of the oceanic crust, and the formation of sedimentary basins on the basis of their relationships to lithospheric plate boundaries. Convection of the mantle is postulated to be the driving mechanism for the movement of lithospheric plates. Measurements of the continents using the Global Positioning System confirm the relative motions of plates. Age determinations of the oceanic crust confirm that such crust is much younger than that of the continents and has been recycled by the process of subduction and regenerated at midoceanic ridges.

polished rod

The uppermost joint in the string of sucker rods used in a rod pump artificial-lift system. The '' '' enables an efficient hydraulic seal to be made around the reciprocating rod string.

Vee-Door

The upside down V-shaped opening in one side of the derrick that enables long pipes and tools to be lifted into the interior of the derrick. This opening is aligned with the slide and catwalk of the rig

buoyancy

The upward force acting on an object placed in a fluid. The '' force is equal to the weight of fluid displaced by the object. '' can have significant effects over a wide range of completion andworkover activities, especially in cases in which the wellbore and tubing string contain liquid and gas. Any change in the relative volumes or fluid levels will change the '' forces.

milling

The use of a mill or similar downhole tool to cut and remove material from equipment or tools located in the wellbore.

coiled tubing drilling

The use of coiled tubing with downhole mud motors to turn the bit to deepen a wellbore.

coiled tubing drilling

The use of coiled tubing with downhole mud motors to turn the bit to deepen a wellbore. Coiled tubing drilling operations proceed quickly compared to using a jointed pipe drilling rig because connectiontime is eliminated during tripping. Coiled tubing drilling is economical in several applications, such as drilling slimmer wells, areas where a small rig footprint is essential, reentering wells and drilling underbalanced.

CI

The value of the separation between two adjacent contours. A net pay isopach map might have a contour interval of 10 feet [3 m], whereas a structure contour map might have a contour interval of 1000 feet [300 m]. Contour intervals are chosen according to the map scale and the amount and distribution of control points.

contour interval

The value of the separation between two adjacent contours. A net pay isopach map might have a contour interval of 10 feet [3 m], whereas a structure contour map might have a contour interval of 1000 feet [300 m]. Contour intervals are chosen according to the map scale and the amount and distribution of control points.

Milankovitch cycles

The variation of the Earth's exposure to the sun's rays, or insolation, that results from variations in the orbit of the Earth and the tilt of its axis, and that might affect climate, sea level and sedimentation. Such variations are thought to occur in distinct time periods on the order of thousands of years. Ice ages might be a consequence of Milankovitch cycles. Milutin Milankovitch (1879 to 1958) was a Yugoslavian mathematician and physicist who specialized in studies of solar radiation and the orbit of the Earth.

vertical lift

The vertical distance between two points in a horizontal or deviated wellbore. Any calculations relating to wellbore pressure or downhole pump performance will be based on the vertical lift rather than the distance traveled through the wellbore.

true vertical depth (TVD)

The vertical distance from a point in the well (usually the current or final depth) to a point at the surface, usually the elevation of the rotary kellybushing (RKB).

hydrostatic head

The vertical height of a fluid column, regardless of the length or other dimensions of that fluid column. For example, a deviated wellbore has a longer length than vertical depth. The veritical height of a fluid column at any point in that wellbore is not a function of its measured depth (MD) along the wellbore axis, but rather its vertical distance or true vertical depth (TVD) to the surface.

Steam chamber

The volume of reservoir in which mobile steam exists for an extended period of time.

erosion

The wearing away of material, usually rock or steel, by the continuous abrasive action of a solids-laden slurry.

overburden

The weight of overlying rock. Rock overlying an area or point of interest in the subsurface.

evening tour

The work shift of a drilling crew that starts in the evening or late afternoon. Drilling operations usually occur around the clock because of the cost to rent a rig. As a result, there are usually two separate crews working twelve-hour tours to keep the operation going.

morning tour

The work shift of a drilling crew that starts in the morning. Drilling operations usually occur around the clock because of the cost to rent a rig. As a result, there are usually two separate crews working twelve-hour tours to keep the operation going.

fingerboard

The working platform approximately halfway up the derrick or mast in which the derrickman stores drillpipe and drill collars in an orderly fashion during trips out of the hole. The entire platform consists of a small section from which the derrickman works (called the monkeyboard), and several steel fingers with slots between them that keep the tops of the drillpipe in place.

elastic limit

The yield point, or the point at which a material can no longer deform elastically. When the elastic limit is exceeded by an applied stress, permanent deformation occurs.

sedimentary rocks

These rocks are formed at the Earth's surface through deposition of sediments derived from weathered rocks, biogenic activity or precipitation from solution. Clastic sedimentary rocks such as conglomerates, sandstones, siltstones and shales form as older rocks weather and erode, and their particles accumulate and lithify, or harden, as they are compacted and cemented. Biogenic sedimentary rocks form as a result of activity by organisms, including coral reefs that become limestone. Precipitates, such as the evaporite minerals halite (salt) and gypsum can form vast thicknesses of rock as seawater evaporates. Sedimentary rocks can include a wide variety of minerals, but quartz, feldspar, calcite, dolomite and evaporite group and clay group minerals are most common because of their greater stability at the Earth's surface than many minerals that comprise igneous and metamorphic rocks. Sedimentary rocks, unlike most igneous and metamorphic rocks, can contain fossils because they form at temperatures and pressures that do not obliterate fossil remnants.

Escape Line or Geronimo Line

This cable provides a rapid escape path for the derrickman should well conditions or massive mechanical failure warrant. It is a steel cable attached to the rig derrick or mast near the work platform for the derrickman. This cable is anchored at surface level away from the mast in a loose catenary profile, and fitted with a handle and hand brake that is stored at the top.

undrained test

This test is one in which the fluid in the sample is not able to flow and equilibrate to imposed pore pressure conditions; the fluid mass remains the same while the fluid volume and pressure will vary.

drained test

This test is one in which the pore fluid in the sample is able to flow and equilibrate to imposed pore pressure conditions; the fluid mass and volume will vary but its pressure will be constant. A drained test could be on a dry sample.

Cementing Operations

This type of operations may be undertaken to seal the annulus after a casing string has been run, to seal a lost circulation zone, to set a plug in an existing well from which to push off with directional tools or to plug a well so that it may be abandoned.

reciprocate

To alternately raise and lower the drillstring, casing string or liner in the wellbore. It is usually limited to 30 to 60 ft [9 to 18 m] of vertical travel in the derrick. The purpose for doing this to the drillstring is usually to clean cuttings and other debris from the wellbore. It can improve the chances of a good cement job in casing or liners.

space out

To assemble components to ensure that all critical length dimensions are met, as is required to ensure that the production tubing can be landed in the wellhead and production packer with the desired weight distribution. The term also may apply to surface pressure-control equipment offshore, where well intervention equipment may be required at certain deck levels.

erode

To cause or undergo erosion, the process of denudation of rocks, including physical, chemical and biological breakdown and transportation. The material from the rocks can be transported by wind, water, ice, or abrasive solid particles, or by mass-wasting, as in rock falls and landslides.

back wash

To conduct reverse circulation, that is, to circulate fluid down the wellbore annulus, with returns being made up the tubing string. Reverse circulation is often used to remove debris from the wellbore since the high fluid flow rate inside the tubing string enables the recovery of large or dense debris particles that are difficult or impossible to remove with conventional circulation.

run in hole (RIH)

To connect pipe together and lower the connected length into the borehole in a controlled fashion. The pipe lengths are usually screwed together either with rotary-shouldered connections for the drillstring, or threaded and coupled connections for casing, liners and most tubing. (ANTONYM come out of the hole)

make up

To connect tools or tubulars by assembling the threaded connections incorporated at either end of every tool and tubular. The threaded tool joints must be correctly identified and then torqued to the correct value to ensure a secure tool string without damaging the tool or tubular body.

tag

To contact, or tag, a known reference point or obstruction in the wellbore with the tubing string, wirelineor other intervention equipment.

log

To continuously measure formation properties with electrically powered instruments to infer properties and make decisions about drilling and production operations. The record of the measurements, typically a long strip of paper, is also similarly named. Measurements include electrical properties (resistivity and conductivity at various frequencies), sonic properties, active and passive nuclear measurements, dimensional measurements of the wellbore, formation fluid sampling, formation pressure measurement, wireline-conveyed sidewall coring tools, and others.

geosteer

To control the direction of a well based on the results of downhole geological logging measurements rather than three-dimensional targets in space, usually to keep a directional wellbore within a pay zone. In mature areas, this action may be used to keep a wellbore in a particular section of a reservoir to minimize gas or water breakthrough and maximize economic production from the well.

core

To deepen the wellbore by way of collecting a cylindrical sample of rock. A core bit is used to accomplish this, in conjunction with a core barrel and core catcher.

drilling core

To deepen the wellbore by way of collecting a cylindrical sample of rock. A core bit is used to accomplish this, in conjunction with a core barrel and core catcher.

sidetrack

To drill a secondary wellbore away from an original wellbore. It may be done intentionally or may occur accidentally.

pack off

To effect hydraulic isolation, either with a sealing device, such as a packer, or with a specialized plasticor fluid, such as a sealing compound.

Underream

To enlarge a wellbore past its original drilled size. This is sometimes done for safety or efficiency reasons. Some well planners believe it is safer to drill unknown shallow formations with a small-diameter bit, and if no gas is encountered, to then enlarge the pilot hole.

underrarm

To enlarge a wellbore past its original drilled size. Underreaming is sometimes done for safety or efficiency reasons. Some well planners believe it is safer to drill unknown shallow formations with a small-diameter bit, and if no gas is encountered, to then enlarge the pilot hole. An underreaming operation may also be done if a small additional amount of annular space is desired, as might be the case in running a liner if surge pressures were problematic.

ream

To enlarge a wellbore. Perhaps the most common reason for performing this process to a section of a hole is that the hole was not drilled as large as it should have been at the outset.

Break Circulation

To establish circulation of drilling fluids after a period of static conditions. Circulation may resume after a short break, such as taking a survey or making a mousehole connection, or after a prolonged interruption, such as after a round trip.

Bullhead Procedure

To forcibly pump fluids into a formation, usually formation fluids that have entered the wellbore during a well control event. Though it is intrinsically risky, it is performed if the formation fluids are suspected to contain hydrogen sulfide gas to prevent the toxic gas from reaching the surface. It is also performed if normal circulation cannot occur, such as after a borehole collapse

stab in

To guide and engage components that are designed to couple, such as a seal assembly in a sealborepacker.

unload

To initiate flow from a reservoir by removing the column of kill fluid from the wellbore. Several methods of '''' the well are used, including circulation of lower density fluid, nitrogen lifting and swabbing. The method used will depend on the completion design, reservoir characteristics and local availability.

scout

To inspect an area or to monitor activity.

Bridge

To intentionally or accidentally plug off pore spaces or fluid paths in a rock formation, or to make a restriction in a wellbore or annulus. It may be partial or total, and is usually caused by solids (drilled solids, cuttings, cavings or junk) becoming lodged together in a narrow spot or geometry change in the wellbore.

rig up

To make rig ready for use. Equipment must typically be moved onto the rig floor, assembled and connected to power sources or pressurized piping systems

strap

To measure a running string or assembled components while running in or out of the wellbore.

bump the plug

To observe the increase in pump pressure indicating that the top cement plug has been placed on the bottom plug or landing collar. '''''' concludes the cementing operation.

fracture

To perform a stimulation treatment, which is routine for oil and gas wells in low-permeability reservoirs. Specially engineered fluids are pumped at high pressure and rate into the reservoir interval to be treated, causing a vertical fracture to open. The wings of the fracture extend away from the wellbore in opposing directions according to the natural stresses within the formation. Proppant, such as grains of sand of a particular size, is mixed with the treatment fluid to keep the fracture open when the treatment is complete. Hydraulic fracturing creates high-conductivity communication with a large area of formation and bypasses any damage that may exist in the near-wellbore area.

complete a well

To perform activities in the final stages of well construction to prepare a well for production. The well is completed once zones of interest have been identified.

racking back pipe

To place a stand of drillpipe in the derrick when coming out of the hole on a trip.

dope OR doping

To place lubricant on drillpipe

stab

To place the male threads of a piece of the drillstring, such as a joint of drillpipe, into the mating female threads, prior to making up tight.

bring in the well

To prepare a well for production by initiating flow from the reservoir. This is the final phase of acompletion or workover process.

plug and abandon (P&A)

To prepare a well to be closed permanently, usually after either logs determine there is insufficient hydrocarbon potential to complete the well, or after production operations have drained the reservoir.

plug and abandon

To prepare a wellbore to be shut in and permanently isolated. There are typically regulatory requirements associated with the P&A process to ensure that strata, particularly freshwater aquifers, are adequately isolated. In most cases, a series of cement plugs is set in the wellbore, with an inflow or integrity test made at each stage to confirm hydraulic isolation

cementing

To prepare and pump cement into place in a wellbore.

Rift (vt.)

To pull apart the Earth's crust.

acidize

To pump acid into the wellbore to remove near-well formation damage and other damaging substances. This procedure commonly enhances production by increasing the effective well radius. When performed at pressures above the pressure required to fracture the formation, the procedure is often referred to as acid fracturing.

Circulate or Circulation

To pump fluid through the whole active fluid system, including the borehole and all the surface tanks that constitute the primary system.

circulate

To pump fluid through the whole active fluid system, including the borehole and all the surface tanks that constitute the primary system.

circulate out

To pump the drilling fluid until a sample from the bottom of the hole reaches the surface. This is commonly performed when drilling has ceased so that the wellsite geologist may collect a cuttingssample from the formation being drilled, or when the driller suspects that a small amount of gas has entered the wellbore.

slip and cut

To replace the drilling line wrapped around the crown block and traveling block. As a precaution against drilling line failure due to fatigue, the work done by the drilling line is closely monitored and limited.

correlate

To seek a comparison or equivalence. Scientists attempt to compare or match up well log signatures, chemical signatures, seismic signatures, fossils and rock samples across wide areas to determine the equivalence, extent, thickness, quality, relative age or other properties of stratigraphic units and rock bodies.

kill

To stop a well from flowing or having the ability to flow into the wellbore. Typically involves circulating reservoirfluids out of the wellbore or pumping higher density mud into the wellbore, or both.

wait on cement (WOC)

To suspend drilling operations while allowing cement slurries to solidify, harden and develop compressive strength. T

wait on cement

To suspend operations while a cement slurry to develops sufficient compressive strength to allow drilling or other wellbore activity to continue. The '' '' '' time is generally used to test the surface pressure-control equipment, such as the BOP stack. Attempting to drill out the float or guide shoe before the cement has developed sufficient bond strength may result in backing off a casing joint.

nipple down

To take apart, disassemble and otherwise prepare to move the rig or blowout preventers.

pinch out

To taper to a zero edge.

make up

To tighten threaded connections.

swab

To unload liquids from the production tubing to initiate flow from the reservoir.

Break Out

To unscrew drillstring components, which are coupled by various threadforms known as connections, including tool joints and other threaded connections.

shoot a level

To use a special acoustic device to determine the fluid level in a conduit or annular space. The principle of operation relies on accurately recording the time taken for a return echo to be bounced from the fluid in contained area.

drill pipe

Tubular steel conduit fitted with special threaded ends called tool joints. They are used to connect the rig surface equipment with the bottomhole assembly and the bit, both to pump drilling fluid to the bit and to be able to raise, lower and rotate the bottomhole assembly and bit

stand

Two or three single joints of drillpipe or drill collars that remain screwed together during tripping operations.

Ultralow interfacial tension

Values of interfacial tension (IFT) less than about 10-2 mN/m. Mixed surfactant systems, as used in enhanced oil recovery, adsorb at the oil/water interface and can be designed to generate an interface that is flexible and that has an ultralow IFT.

Volumetric sweep efficiency

Volumes of oil contacted by the displacment agent as a fraction of the volumes of original oil in place

clear brine

Water containing more dissolved inorganic salt than typical seawater.

clear brine

Water containing more dissolved inorganic salt than typical seawater. Saline liquid usually used in completion operations and, increasingly, when penetrating a pay zone.

connate water

Water trapped in the pores of a rock during formation of the rock. The chemistry of connate water can change in composition throughout the history of the rock. Connate water can be dense and saline compared with seawater. Formation water, or interstitial water, in contrast, is simply water found in the pore spaces of a rock, and might not have been present when the rock was formed. Connate water is also described as fossil water.

stylolite

Wave-like or tooth-like, serrated, interlocking surfaces most commonly seen in carbonate and quartz-rich rocks that contain concentrated insoluble residue such as clay minerals and iron oxides. Stylolites are thought to form by pressure solution, a dissolution process that reduces pore space under pressure during diagenesis.

Bacteria that can live with or without oxygen and produce mats of high-density slime that cover surfaces. Their primary detrimental effects are the protection of sulfate-reducing bacteria and pore plugging.

What are slime forming bacteria and what detrimental effects do they have on the reservoir?

Crown Block and Traveling Block

What are the two large block on a drilling rig called? These are a set of pulleys used to gain mechanical advantage in lifting or dragging heavy objects

Expressed in units of feet per minute or, less commonly, meters per minute.

What are the units for Annular Velocity?

(2) A significant increase in the Bond number and therefore that gravitational forces (i.e., buoyancy) can mobilize additional oil.

What are two implications of ultralow IFT for oil recovery?

Acetylene

What chemical is commonly used as a tracer gas for the Carbide Lag Test?

Local displacement efficiency

What does LDE stand for?

Minimum miscibility enrichment

What does MME stand for?

Pressure, volume, temperature

What does PVT stand for?

Special core analysis laboratory

What does SCAL stand for?

Stock tank oil initially in place

What does STOIIP stand for?

Stock tank original oil in place

What does STOOIP stand for?

Thermally enhanced oil recovery

What does TEOR stand for?

Abbreviation for mils (thousandths of an inch) per year penetration, a unit of measurement for the corrosion rate of a coupon.

What does mpy stand for?

millions of years before present

What is MYBP

Around 0.25 in. in diameter

What is a common hole size for bit nozzles?

A barrier or resistance to the flow of injected steam formed by a volume around a producing well in a steam flood that contains high oil and liquid water saturation. This is typically maintained by choking the production well to keep the surrounding formation just below saturated steam temperature and pressure conditions.

What is a steam trap and how may it be maintained?

In a ternary diagram, a graphical representation of two fluids being mixed. The ends of the tie line indicate the compositional concentrations of the two mixed fluids. The composition of the mixture lies on the line, with its position dependent on the concentration ratio of the two end-point fluids.

What is a tie line?

A type of damage in which the formation wettability is modified, generating a change in relative permeability that eventually affects well productivity.

What is a wettability change?

Barefoot Completion

What is another name given to openhole completion or without casing completion?

shoe joint OR shoe track

What is another term for float joint?

A low mobility ratio is better as it means less viscous fingering and better sweep

What is better, a high or low mobility ratio?

The well is shut in for several days to allow uniform heat distribution to thin the oil.

What is involved in the soak phase of cyclic steam injection?

The Gibbs free energy per unit area of interface at fixed temperature and pressure is termed either interfacial tension or surface tension. The term "interfacial tension" is used when the interface is between two immiscible liquids. The term "surface tension" is used when one of the phases is air and the other is liquid.

What is the difference between interfacial tension and surface tension?

The name mud acid was given to these mixtures because they were originally developed to treat damage from siliceous drilling muds.

What is the origin of the name mud acid?

To displace reservoir brine containing potassium, sodium, calcium and magnesium ions from the near-wellbore area, avoiding adverse interactions with the chemical solution. The other purpose is to adjust reservoir salinity to favorable conditions for the surfactant.

What is the purpose of a preflush in chemical flooding?

chlorite

[(Mg,Al,Fe) 12(Si,Al) 8O20(OH) 16] A platy, pale green mineral of the mica group of sheet silicates, also considered to be a type of clay mineral, found in sedimentary and low-grade metamorphic rocks. Chlorite is a common authigenic mineral lining the pores of sandstones. In some cases, the presence of authigenic chlorite on sand grains can inhibit the growth of pore-filling cements during diagenesis and preserve pore space for occupation by hydrocarbons.

barite

[BaSO4] A dense sulfate mineral that can occur in a variety of rocks, including limestone and sandstone, with a range of accessory minerals, such as quartz, chert, dolomite, calcite, siderite and metal sulfides. Barite is commonly used to add weight to drilling fluid. Barite is of significance to petrophysicists because excess barite can require a correction factor in some well log measurements.

gypsum

[CaSO4 72H2O] A highly insoluble sulfate mineral that is the first to precipitate from evaporating seawater. Dehydration of gypsum can produce anhydrite. Fine-grained gypsum is called alabaster.

salt

[NaCl] A soft, soluble evaporite mineral also known as halite or rock salt. Because salt is less dense than many sedimentary rocks, it is relatively buoyant and can form salt domes, pillars or curtains by flowing and breaking through or piercing overlying sediments, as seen in the Gulf of Mexico and the Zagros fold belt. Halite can be critical in forming hydrocarbon traps and seals because it tends to flow rather than fracture during deformation, thus preventing hydrocarbons from leaking out of a trap even during and after some types of deformation.

halite

[NaCl] A soft, soluble evaporite mineral commonly known as salt or rock salt. Because salt is less dense than many sedimentary rocks, it is relatively buoyant and can form salt domes, pillars or curtains by flowing and breaking through or piercing overlying sediments, as seen in the Gulf of Mexico and the Zagros fold belt. Halite can be critical in forming hydrocarbon traps and seals because it tends to flow rather than fracture during deformation, thus preventing hydrocarbons from leaking out of a trap even during and after some types of deformation.

Clays

a fine-grained natural rock or soil material that combines hydrous aluminum silicates whose molecular lattice can also contain magnesium, pottasium , sodium and iron

frac fluid

a fluid injected into a well as part of a stimulation operation. Fracturing fluids for shale reservoirs usually contain water, proppant, and a small amount of nonaqueous fluids designed to reduce friction pressure while pumping the fluid into the wellbore. These fluids typically include gels, friction reducers, crosslinkers, breakers and surfactants similar to household cosmetics and cleaning products; these additives are selected for their capability to improve the results of the stimulation operation and the productivity of the well.

structural steering

a method of directing the wellbore trajectory of horizontal wells using 3D visualization. It is the process of combining structural analysis and modeling capabilities with borehole images to optimize well placement, often in real-time. Structural steering integrates deep-reading LWD resistivity tools and high-resolution imaging devices to create structural models of often complex geologic conditions encountered by the drill bit. This technique helps operators understand the formations already drilled and allows them proactively to correct wellbore trajectories for anticipated changes.

rotating control device

a pressure-control device used during drilling for the purpose of making a seal around the drillstring while the drillstring rotates.

water cushion

volume of water placed in a tubing string prior to conducting a drillstem test or opening a well to flow. is designed to reduce and control the pressure drawdown applied to the reservoirwhen the downhole valve or tester valve is opened to initiate flow.