Chapter 7 - Oil and Gas
4 essential prerequisites for accumulations of petroleum to occur:
1) There must have been a suitable source of marine deposits contained within the source rocks. (2) These rocks must have allowed for the lateral movement of petroleum deposits via a permeable pathway to layers of porous and permeable reservoir rock. (3) The reservoir must be sealed at the top by an impermeable layer or caprock. (4) A trap must be present to prevent the lateral migration of the petroleum away from the reservoir.
3 types of structural traps
1. Anticline - most common, formed by the folds of Earth´s geological strata and when occurring in large structures can hold appreciable amounts of petroleum in place, e.g. Ghawar in KSA 2. Fault - formed when a reservoir rock is brought into contact with impermeable strata by a movement along the geological fault within the Earth's crust 3. Salt dome - is a dome-shaped formation of rock salt that has been forced upwards through overlying strata until it lies under a caprock.
oil price shocks of 1973 and 1979
1. In October 1973 a long-simmering war between Israel and its neighbours Egypt and Syria broke out, the Yom Kippur war. - This was of global importance since Israel had the backing of the USA while Egypt had the backing of the Soviet Union. The Arab members of OPEC decided to use 'the oil weapon' in support of Egypt and Syria. They announced price rises and production cuts, which would increase every month. - A peace deal between the warring countries was eventually brokered in January 1974. Some of the production cuts were lifted but oil prices did not fall. It had become obvious that the world could afford to pay more for its oil. The average price for 1974 was three times what it had been in 1973. 2. Then in 1979 came the Iranian Revolution. The country's oil output (about 8% of the global total) dropped dramatically. Matters got worse in the following year, 1980, when the neighbouring country of Iraq attacked Iran, destroying much of the oil infrastructure. The world oil price peaked in January 1981 at nearly ten times in real terms what it had been in the summer of 1970. Although subsequent extra supplies of oil from the North Sea, Russia and Alaska reduced the world oil price, the price rises of 1973 and 1979 have had a profound effect on oil consumption across the globe,
LNG - advantage and disad
- Although this requires considerable capital investment in refrigeration plant and storage, it does allow cheap long-distance transport by sea. - Many impurities must be removed from the gas before cooling, not least those that would actually freeze solid at the extreme temperature. - The refrigeration process of course requires energy, equivalent to about 10% of that of the final LNG. - At the receiving end further energy is required to convert the liquid back into a gas before it can be distributed. - At Grain this energy comes in the form of waste heat from an adjacent gas-fired power station. - This extra energy use means that LNG has a higher overall CO2 emission factor than natural gas produced closer to the consumer, but not sufficiently high to make it unattractive.
Gas to liquids (GTL)
- Liquid fuels can be easily transported by tanker. Natural gas requires pipelines or expensive liquefaction plants to manufacture LNG. - There are many places in the world that have natural gas available, but which don't have the capacity to export it. - Gas to liquids conversion has become increasingly attractive as oil prices have risen -1. reversing methanation reaction- Methane can be converted to synthesis gas by steam reforming: meth ane + steam → carbon monoxide + hydrogen - One convenient transportable liquid chemical that can then be produced from this is methanol . This is a valuable chemical feedstock and can be used directly as a vehicle fuel (although it is highly toxic) and it can also be further processed into petrol. 2. to use the synthesis gas to feed a Fischer-Tropsch reaction, as in the Sasol CTL plants.
Lurgi gasifier and prod of synthetic gas
- In the Lurgi gasifier, coal is fed automatically into the top of the pressure vessel (through an airlock) and distributed evenly through it by a coal distributor. - A mixture of steam and oxygen is introduced through a rotating grate at the bottom of the gasifier, where ash is also removed through another airlock. - The resulting gas is then cooled and the unwanted ammonia, tars and oils are removed. - What remains is useful synthesis gas or 'syngas' (carbon monoxide and hydrogen) plus some methane and CO2 and unwanted sulfur compounds, such as hydrogen sulfide. - These sulfur compounds are removed by amine scrubbing or a similar process as described earlier in Box 7.6. The clean synthesis gas can be used to make a whole range of possible end products
ways of coping peak demands of NG especially in winter and bad weather
- The gas wells and the pipeline systems, including the international connections, thus have to cope with a highly variable flow. 1. A large amount of GAS STORAGE is obviously highly desirable as well.This can be achieved by RE:INJECTING THE GAS INTO A DEPLETED FIELD, e.g. UK main storage is the offshore Rough field, off the north-east coast of England, 2. use of INTERRUPTIBLE CONTRACTS for industry and other large users. They are offered gas at a reduced price, but on condition that the supply can be turned off, usually with several days notice. Often these users keep their own back-up supplies of alternative fuels such as heating oil.
pipelines have to cross national borders creates interesting problems.
- The bulk of Russian gas exports to Europe have to pass through Ukraine or the neighbouring state of Belarus. There have been regular disputes between Russia, Ukraine and Belarus over the price of gas supplies to them with threats to 'turn the tap off' if payment isn't made. . This is difficult since contracted gas supplies have to continue to those countries on the far side who are prepared to pay their bills. - A notable new feature of the gas map is thus a new proposed pipeline under the Baltic Sea from Russia directly to Germany. When completed this will be the longest undersea gas pipeline in the world.
light distillate
-is arguably the most important of the petroleum fractions. - It has products with boiling points in the range 70-200 °C, such as petrol (or motor spirit or gasoline), the light chemical feedstock called naphtha (pronounced 'naftha'), kerosene, jet fuel and paraffin.
heavy distillate,
- The least volatile of the petroleum fractions as those constituents of crude oil with a boiling point above 350 °C. Heavy distillate is either solid or semi-solid normal temperatures and may require heating to encourage free flow. - Diesel fuel for large ships' engines - marine diesel - falls on the boundary of middle and heavy distillate. In volume terms the most significant product falling within this range has been 'fuel oil' used both for power stations and the largest industrial boilers.
naphtha
. This is one of the light distillates produced from the refining of oil and consists of molecules containing between five and twelve carbon atoms.
heavy and extra heavy oil
- buried petroleum depoosit so thick and viscousd that it will not flow to the ES under natural reservoir process - as in tertrary recovery of lighter crude oil, it is necessary to inject steam into the production wells to heat the oil and force it to the surface, after which processed and refined -with high sulrfur and need to be refined out
middle distillate
- is defined by the products with boiling points in the temperature range 200-350 °C. The two most recognizable oil products are diesel fuel, colloquially referred to as 'DERV' (Diesel Engined Road Vehicle), and an overlapping fraction known as 'gas oil', which is mainly used as burning oil for domestic and light commercial heating. Gas oil, as its name suggests, was originally used to provide hydrocarbon en richment in the manufacture of town gas.
composition of natural gas
- natural gas may not be completely pure. Often associated gas is 'wet' and wells produce a mixture of natural gas, condensate and natural gas liquids (NGL). - The are li
shale oil
- organic material in sedimentary rocks are heated and matures into oil or NG. however, some are in immature state, wayx solid as KEROGEN. - shale rocks consisted of layers of mud , compressed into flat , hard sheets , where kerogen remains trapped are oil shales. - overall energy content low - questions the overall energy balance of the whole process ( EROEI)
fractionation
- process of separating the alkanes in crude oil by distillation into different fractions. - The different boiling points of the alkanes in crude oil allow it to be separated by distillation into various oil fractions.
steps in oil production
- survey for oil-bearing rocks - drilling - if drilling confirms the presence of oil, - attempt to determine the volume of oil contained, the extent of the field, and its likely productivity. - To achieve this it is necessary to drill further appraisal wells. - A number of these may be required in order to obtain sufficient information. - Should full development then be considered appropriate, a series of production wells will be sunk.
alkanes
- the main components of natural gas and petroleum. - Methane, CH4, is the simplest possible alkane and is the main constituent of natural gas. - Others consist of chain molecules, though these are not necessarily all straight chains - For many alkanes there may be different isomers with the same chemical formulae but with different arrangements of branching chains and with slightly different properties. - Generally the larger the molecule, the higher the boiling point and the lower the energy density.
Is CTL the answer to peak oil?
1. Is it likely to be economic? - While cheap coal is widely available, natural gas is more difficult to transport and GTL plants are really only economic for those who have a surplus, such as Qatar. Even then, t he development of the world trade in liquefied natural gas may make direct gas sales more profitable. 2. What are the CO2 emission consequences? - A litre of petrol or diesel emits CO2 when it is eventually burned. The difficulty with CTL and GTL projects is that even more CO2 is released in the manufacture of the fuel. The term well-to-wheels is used to describe the full pathway of production and use of a vehicle fuel. Fuel from CTL is likely to have at least twice the CO2 emissions per litre of conventional fossil-derived fuel. The figure for GTL is about 50% extra. However, the indirect CTL process (using synthesis gas) does offer the possibility of separating some of the CO2 making it available for sequestration. 3. Is there enough water and coal? - The indirect CTL process is one of 'adding hydrogen' and it requires a large amount of good quality water to supply it. To summarize, it would seem that the large-scale adoption of CTL could have serious environmental effects on both global CO2 emissions and water resources, and could place a considerable strain on global coal supplies. On the more positive side there are possibilities of using carbon capture and storage in indirect conversion plants.
cracking technologies - GETTING MORE FROM crude oil
1. THERMAL CRACKING, applying heat to the heavy distillate and residuals. 2. techniques employed catalysts such as aluminium silicates in CATALYTIC cracking to reduce the temperatures required . (A catalyst is a substance that assists a chemical reaction, but remains unchanged itself.) 3. HYDROCRACKING - The overall hydrogen content of the products for which there is a demand is higher than that of crude oil. -Thus some process of 'adding hydrogen' is necessary. As described in Chapter 5, hydrogen can be made by spraying water onto red-hot coke (it can be petroleum coke in this case). - By heating heavy oil to a high temperature under pressure in the presence of hydrogen and using a suitable catalyst, new lighter fractions of oil can be produced. 4. , increasingly the demand is for very low sulfur fuels, while a supply of 'sour' crude may contain 5% sulfur. HYDROTREATING, a similar process to hydrocracking, converts the sulfur content to the gas hydrogen sulfide. - This can be removed and treated, ending up as elemental sulfur, which can be used in fertilizer manufacture. Oil refining and natural gas processing are the world's largest commercial sources of sulfur. 5. The amount of hydrogen added to oil in a refinery can be significant and gives rise to REFINERY GAIN, with more barrels of product emerging from a refinery than the number of barrels of crude oil that entered it. 6. A refinery may produce a range of possible hydrocarbons from basic refining and cracking. The end products are likely to be achieved by blending mixtures of more than one fraction or subfraction in order to optimize the characteristics. For example, as will be described in Chapter 8, petrol must have the best possible octane rating, while diesel fuel must have the correct compression ignition characteristics.
synthetic gas from coal process
1. The first step in the production of either methane or hydrogen is the partial combustion of coal in a limited supply of air or oxygen. The main product is carbon monoxide: 2C + O2 → 2CO carbon + oxygen → carbon monoxide This is an exothermic reaction, i.e. it creates heat - this partial combustion creates PRODUCER GAS - WIDELY USED TO FUEL VEHICLES WWII 2. If a supply of steam is added to the oxygen then the water gas reaction can also be carried out: C + H 2 O <--> CO + H2 - This is an endothermic reaction, i.e. it absorbs energy and has the effect of cooling the coal down. - It needs a high temperature of around 1000 °C to proceed satisfactorily. Since this is a potentially reversible reaction, it is ritten here with a 'two-way arrow'. - These processes are often carried out on an industrial scale in a Lurgi gasifier.
range of geophysical techniques are employed to decide whether an area is likely to contain suitable oil-bearing rocks. - three geophysical survey techniques used to determine whether a petroleum-bearing formation is likely to be present in any particular area.
1. gravimetric survey - looking at local variations in the Earth's gravitational field - Oil-bearing, sedimentary rocks are generally far less dense than other types and effectively reduce the Earth's gravitational pull within the locality. - A substantial thickness of sediments can thus be located by measuring the Earth's gravitational field and searching for a low reading. Gravimetric surveys are far from infallible, but they are cheap and speedy to conduct. 2. geomagnetic survey of a region- looking at variations in the Earth's magnetic field Non-sedimentary base rocks frequently contain large amounts of ironrich minerals and are consequently magnetic. As such they can easily be distinguished from sedimentary rocks. 3. seismic survey- projecting shock waves down into the ground. Gravity and magnetic surveys may accurately detect the presence of sedimentary formations but they cannot detect the presence (or absence) of oil-bearing traps within the rock strata. - The seismic method is based on recording the time taken for sound waves to travel from a source at the Earth's surface down into rocks below, reflect off a rock boundary, and travel back to surface detectors.
Why are oil and gas so special?
1. have a high energy density 2. are clean to burn (compared to coal) 3. are convenient and easy to use - Compared to lighting a coal fire, or even worse, starting up a steam engine, oil and gas are extraordinarily easy to use (and to turn off). 4. are readily available and (for the moment) cheap. easy ditribution,storage, protability - Liquid fuels can be pumped (though really heavy fuel oil may need to be heated first). Oil pipelines run for thousands of kilometres across the globe including under the sea. Oil can be transported long distances cheaply by tanker (a sea journey of 5000 km may cost only about US$1 per barrel). - Crude oil and natural gas are globally traded commodities, as are standard petrol and diesel fuels. They have been readily available for many years.
compostion of natural gas
1. it may contain useful NATURAL GAS LIQUIDS that are condensed out. There may also be some ethane (C2H6) present. This is commonly extracted and used as a feedstock for plastics, but often a certain amount is left in the natural gasmixture. 2. contain contaminant HELIUM; which is widely used in medical equipment and for low temperature applications, such as Superconducting magnets. The natural gas industry is the world's largest supplier. 3. Other contaminants are not so benign. - Sour gas contains sulfur in the form of hydrogen sulfide (H2S). Acid gas contains CO2. These contaminants can be removed by washing the gas with organic amine chemicals, such as monoethanolamine (MEA), which react with them.This is known as amine scrubbing. The amines are pumped away and then regenerated by heating, releasing the H2S for conversion into sulfur and CO2. The sulfur can be sold for fertilizer use and the CO2 used for reinjection into the gas well to flush out yet more gas. Their removal also reduces the amount of corrosion to steel pipework. Gas that doesn't have these contaminants is known as sweet gas.
several ways of classifying different useful fractions obtained from crude oil
1. light', 'middle' and 'heavy' distillate. 2. two further components - At the top of the column there are GASES TOO VOLATILE TO CONDENSE (e.g. propane, butane). - At the bottom are the RESIDUALS consisting of the very heavy tars remaining after the 'fractions' have been distilled off. These are too dense to rise up the column. - They are far from useless, however, and indeed some of the most vital of all oil products are obtained from the very bottom of the barrel, usually by steam or vacuum distillation. They include paraffinic waxes and various grades of lubricating oils. Nothing is wasted, and what then remains is used as either heavy fuel oil, bitumen for road-making, or solid 'petroleum coke', useful either for simple steam raising or even as a source of graphite.
three Ps - oil and gas reserves terminology
1. proven reserves (1P or P90): - those with a high probability (>90%) of being economically recovered 2. proven and probable reserves (2P or P50): - the total reserves, including the proven (IP) reserves, with a medium overall probability (>50%) of being economically recovered 3 . proven, probable and possible reserves (3P or P10): - the total reserves,including the 2P reserves, with only a low overall probability (>10%) of being economically recovered. 4. The 'undiscovered' resources at the right are often called 'yet-to-find'.
Coal to liquids (CTL)
1. removing carbon by low-temperature carbonization, atype of coal processing that produces town gas plus a range of liquid hydrocarbons. 2. Adding hydrogen - direct liquefaction 3. Adding hydrogen - the Sasol process, Rather than adding hydrogen directly to coal, this first breaks the coal down into synthesis gas and then builds up heavier hydrocarbon molecules from it using the Fischer-Tropsch (FT) process.
converted products
1. town gas from oil 2. petroleum, synthetic natural gas or hydrogen from coal 3. petroleum from natural gas. - but costly - Coal-to-liquids (CTL) in particular has been carried out on a large scale in Germany during the 1930s and 1940s and in South Africa from the 1950s to the present day. - The manufacture of synthetic natural gas (SNG) from coal is carried out in the USA, and - in Malaysia a gas-to-liquids (GTL) plant turns a surplus of natural gas into petroleum.
how do the oil companies take into account both changing crude inputs and changing product demand in the refining process?
A fundamental problem is that the greatest demand is for light products, such as petrol, while the crude oil supply tends to consist more of lower, heavier constituents. - So refining techniques known as cracking were devised to break down the larger (heavy) hydrocarbon molecules into smaller (lighter) ones. - Where this is used for 'heavy oils' and 'oil sands' it is sometimes called upgr ading.
traditional gas boiler
A traditional gas boiler consists of a gas burner heating the water circulated in a central heating system. The hot flue gases are normally just vented and the hot water vapour from the combustion of the gas is lost.
Biofuels
Biofuels are liquid fuels derived from biomass, including ethanol and biodiesel. In 2009 world production was equivalent to just over 1% of the other forms of oil.
crude oil
Crude oil made up about 84% of the oil produced in 2009; it is a mixture of hydrocarbons that exist in a liquid phase at atmospheric pressure and room temperature.
Organisation of Petroleum Exporting Countries (OPEC)
In 1960 some other producers - Iran, Iraq, Kuwait, Saudi Arabia and Venezuela - set up the Organisation of Petroleum Exporting Countries (OPEC) to 'secure fair and stable prices for petroleum producers'. They were later joined by a number of other, mainly Middle Eastern, countries.
methanation
In the final stage, methanation, carbon monoxide is reacted with hydrogen in the presence of a nickel catalyst to produce methane and steam: carbon monoxide + hydrogen → methane + steam The reaction is exothermic and proceeds spontaneously.
water gas shift reaction
In the route to make methane or hydrogen, the next stage is the so-called water gas shift reaction, in which some of the carbon monoxide is reacted with steam to produce CO2 and hydrogen: carbon monoxide + water ↔ carbon dioxide + hydrogen
Liquefied petroleum gases (LPG)
Liquefied petroleum gases (LPG) are those such as propane and butane which can be liquefied under mild pressure at room temperature. They are commonly sold for cooking, lighting and transport uses.
blow-out preventer (BOP)
Modern wells are normally equipped with a blow-out preventer (BOP) to contain any sudden rush of high-pressure oil or gas. The explosion on the BP Deepwater Horizon oil rig described in Chapter 1 (see Figure 1.23) was in part due to the failure of a BOP to operate.
two ways of getting a good energy density per unit volume from natural gas
Natural gas has a high energy density in terms of its mass (i.e. MJ per kilogramme). However, there are only two ways of getting a good energy density per unit volume, 1. COMPRESSING 2. LIQUEFYING - Compressed natural gas (CNG) is often used in road vehicles at pressures of up to 300 atmospheres. - Natural gas canbe liquefied by cooling it to -162 °C. Although this is an extremely low temperature it can then be stored at atmospheric pressure. - LNG has only about half the energy density of crude oil, but it can be transported in insulated tanker ships (Figure 7.19(a)) and stored in large insulated tanks,
natural gas
Natural gas has an even higher energy density and lower CO2 emissions, but being a gas is only used for transport applications as compressed natural gas (CNG).
oil types
Oil, as shown in the statistics of Tables 7.3 and 7.4, consists of crude oil, natural gas liquids (NGLs), condensates and unconventional oil, but doesn't include biofuels or refinery gains.
Town gas from oil process
PRODUCING TOWN GAS FROM NAPTHA 1. By treating these with high-pressure steam at a high temperature (around 700 °C), a process called steam reforming, the carbon-carbon bonds could be sheared completely, producing a gaseous mixture containing carbon monoxide and hydrogen (and a little methane). For example, starting with pentane: C5H12 + 5H2 O → 5CO + 11H2 pentane + steam → carbon monoxide + hydrogen
Petroleum formation
Petroleum - rock oil - Abundance of plant and animal life and a seabed environment that discourages breakdown of dead organic material by bacterial action or oxidation - Compressed by thick layers of marine mud and silt, preserves the material - Temp and pressure increases as depth increases - Chemical processes takes place, forming oil at about 100 degrees C - Higher temperatures favour the formation of gas. - Given the high temperature underground, they are likely to migrate to water-bearing aquifers in permeable rock ( reservoir rock) - And prevented to seep upwards by a caprock, an impermeable seal - Lateral migration is reduced by the geological traps within the reservoir beds. - One type of geological trap is the STRUCTURAL TRAP
sweet and sour gas
Sour gas contains sulfur in the form of hydrogen sulfide (H2S). - Acid gas contains CO2. These contaminants can be removed by washing the gas with organic amine chemicals, such as monoethanolamine (MEA), which react with them.This is known as amine scrubbing. - The amines are pumped away and then regenerated by heating, releasing the H2S for conversion into sulfur and CO2. - The sulfur can be sold for fertilizer use and the CO2 used for reinjection into the gas well to flush out yet more gas. - Their removal also reduces the amount of corrosion to steel pipework. - Gas that doesn't have these contaminants is known as sweet gas.
Tackling future transport emissions is a potentially difficult task. Some technical possibilities are:
Tackling future transport emissions is a potentially difficult task. Some technical possibilities are: ■ more efficient road vehicles and aircraft ■ more use of biofuels and a possible future 'hydrogen economy' ■ increased use of electric vehicles and a future fully electrified railway system, particularly for freight.
There are three stages and recovery processes of oil, which are increasingly effective.
The third of these makes use of the CO2 from the carbon capture and storage (CCS) process (which will be discussed in Chapter 14 of the textbook) to enhance the oil recovery process. • Primary recovery - high-pressure oil or gas is struck from drilling, then capped off or distributed directly for use through pipeworks. • Secondary recovery - the remaining oil or gas is raised in pressure by using pumps or injecting with unwanted gas or water. This can take many years. • Tertiary recovery or enhanced oil recovery (EOR) - steam, CO2 or nitrogen is injected into the reservoir. This takes much energy because the remaining oil is thick and viscous.
types of natural gas
a) associated gas - found with petroleul b) can also be found on its own, non-associated gas c) Conventional' gas generally flows freely from the reservoirs d)'unconventional' gas, which is more difficult to extract. This is in the form of tight and shale gas, coal bed methane and methane hydrates.
unconventional oil and gas
crude oil recovered by all other methods and from other sources which have many features in common - heavy and extra heavy oil - shale oil - oil or tar sands - unconventional form of oil -biofuels bioethanol and biodiesel -unconventional methane gas
density
density describes the mass per unit volume of a substance
energy content of crude oil
energy content of an 'average' tonne of crude oil is 1 tonne of oil equivalent. As pointed out in Chapter 2, this is equal to 41.868 GJ (often rounded to 42 GJ though many sources use 41.88 GJ).
where do modern-day petroleum deposits occur?
in sedimentary basins - areas within the Earth's crust where layers of rock and marine sediment are known to have accumulated over time. - Gulf of Mexico, North Sea, off the coast of Brazil, Arctic ( next)
CONDENSATE
is a light oil that may contain hydrocarbons such as pentane (C5H12) and is often regarded as part of 'conventional oil'.
One of the attractions of natural gas
t it is sufficiently CLEAN-BURNING that this water vapour can be condensed, recovering its latent heat of vaporization. - In a condensing boiler , this is done by making the heat exchanger sufficiently large so that the return water from the heating system, which may be at about 40 °C, can cool the flue gas to below 50 °C. - This can increase the amount of heat extracted from the gas and increase the overall boiler efficiency to over 90%
cycle of discovery and production of both oil and gas fields:
the North Sea is an example of the cycle of discovery and production of both oil and gas fields: ■ a rapid phase of exploration and discovery ■ a rapid phase of production (to extract the maximum financial value) ■ a declining phase of discovery ■ falling reserves and declining production.
natural gas liquids
these are lighter hydrocarbons such as propane (C3H8) and butane (C4H10). These have sufficiently high boiling points that they can be liquefied at room temperature under pressure and are then sold as liquefied petroleum gas (LPG).
specific volume
volume per unit mass is known as the specific volume ( inverse of density
