Geology 15
What is the upper limit for the Poisson's ratio? (Hint - look at the formula for the Poisson's ratio and set Vs = 0) a. 1 b. 2 c. .5 d. .65 e. .35
.5
Rock has a P-wave velocity (Vp) = 3500 m/s and S-wave velocity (Vs) = 1750 m/s. What is the Poisson's ratio of the rock? a. ½ b. ¼ c. 2/3 d. 1/3 e. ¾
1/3
Dry gas is defined at the one that contains: a. More than .1 gal/1000 ft3 of water vapor b. Less than .25 gal/1000 ft3 of water vapor c. Less than .3 gal/1000 ft3 of water vapor d. Less than .1 gal/1000 ft3 of water vapor e. More than .15 gal/1000 ft3 of water vapor
Less than .1 gal/1000 ft3 of water vapor
Out of the following, which one would you would consider to be a dry gas? a. Ethane b. Butane c. Methane d. Isobutane e. Isopentane
Methane
Introduction of geophysical techniques revolutionized the methods of petroleum exploration during the modern era a. True b. False
True
Magnetic method of geophysical exploration provides a quick and cost-effective way to delineate structural traps a. True b. False
True
Rapid rate of sedimentation in most deep-sea environments which does not allow deep sediments to normally dewater and compact is one of the major causes of overpressure: a. True b. False
True
The gas-hydrates are composed mostly of methane a. True b. False
True
The spontaneous potential (SP) and electric logs could be used in calculating the water saturation a. True b. False
True
Time-lapse or 4D seismology has gained popularity in recent years as allows detection of the movements of the subsurface fluids during production: a. True b. False
True
Regional isohaline maps across sedimentary basins are used by geologists because a. Areas of high salinity must be avoided in exploring for hydrocarbons b. Areas of anomalously high salinity are presumably stagnant regions unaffected by meteoric flow, where oil and gas accumulations may have been preserved. c. The geologists must concentrate on exploring the parts of the basis where the salinity is low because they are the areas with high probability of finding oil and gas.
Areas of anomalously high salinity are presumably stagnant regions unaffected by meteoric flow, where oil and gas accumulations may have been preserved.
Electromagnetic (EM) methods of geophysical exploration are sensitive to the variations of which property of the subsurface? a. Density b. Seismic velocity c. Conductivity/resistivity
Conductivity/resistivity
What happens to the Poisson's ratio when 100% brine saturated rock is replaced with 100% gas? a. Decreases b. Increases c. Stays about the same
Decreases
Gravity method of geophysical exploration is sensitive to the variations of what subsurface property? a. Electrical conductivity b. Seismic velocities and density c. Density d. Magnetic Susceptibility e. Resistivity
Density
Gamma ray (GR) logs are typically used in discriminating between the sand and shale: a. True b. False
True
What is the meaning of a "stratigraphic unit" used in seismic sequence analysis? a. Strata of different rocks. b. A given rock formation that is clearly visible on the seismic reflection records. c. A set of mutually intersecting rock formations visible on the seismic reflections. d. A relatively conformable succession of genetically related strata bounded at its top and base by unconformities.
A relatively conformable succession of genetically related strata bounded at its top and base by unconformities.
Isotherms are defined as the contours of constant temperature in the subsurface. In general, it is observed that they are seldom horizontal. The reason for it is a. Non-planer geometry of the sediments b. Movement of fluids c. Regional variations in heat flow d. A and B only e. A and C only f. A, B, C
A, B, C
Prestack seismic reflection amplitudes as a function of reflection angle are sensitive to the variations in a. P-wave velocity b. S-wave velocity c. Density d. All of the above
All of the above
What are the criteria for commercial oil (hydrocarbon) accumulation? a. Existence of an organic rich source rock b. Source rock must be sufficiently heated to yield petroleum c. There must be a reservoir with sufficient porosity and permeability to contain the hydrocarbon d. The reservoir must be sealed by an impermeable rock to prevent the hydrocarbon from moving upward e. The source, reservoir, and the seal must be arranged such that the petroleum is trapped. f. All of the above
All of the above
What is the primary objective of seismic sequence analysis? a. Interpret different sequence boundaries from seismic reflection data. b. Relate the sequence boundaries with the sedimentary history. c. Study how the basin was formed over time. d. All of the above
All of the above
When a well is being drilled, the parameters that may indicate abnormal pressure are a. A rapid increase in the rate of penetration b. A rapid increase in the temperature of the drilling mud c. A decrease in the density of shale cuttings d. All of the above
All of the above
What Poisson's ratio would you expect for an overpressured formation? Hint-overpressured formations are filled with water. a. Moderate (.2-.3) b. Anomalously low (.05-.15) c. Anomalously high (above .4)
Anomalously high (above .4)
What are the regions of abnormally high heat flow on earth? a. Convergent plate boundaries (subduction zones) b. Divergent plate boundaries (Mid-oceanic ridges) c. Passive ocean margins d. All over the continents
Divergent plate boundaries (Mid-oceanic ridges)
Although the salinity in general increases with depth, there are instances of reversal of this general trend. Such a reversal can happen if (A) meteoric water is trapped beneath an unconformity as a paleoaquifer, (B) rainwater still trapped underground as a paleoaquifer, and (C) there is an overpressured zone: a. A only b. B only c. C only d. Either A or C e. Either A or B f. Either B or C g. Either A or B or C
Either A or B or C
How an idea about existence of overpressure could be obtained in wildcat areas with minimal well control? a. From the Bouguer gravity anomaly b. From the magnetic anomaly c. From the subsurface velocities estimated from seismic data d. From the subsurface resistivity estimated from the electromagnetic data
From the subsurface velocities estimated from seismic data
Salinity of the subsurface water: a. Generally decreases with depth b. Stays nearly constant c. Generally increases with depth
Generally increases with depth
How the density of oil is generally express in the oil and gas industry? a. In kg/m3 b. In lb/ft3 c. In g/cm3 d. In API units e. In lb/gal
In API units
When the P-to S-wave velocity ratio (Vp/Vs) increases, the Poisson's ratio a. Increases b. Decreases c. Does not change
Increases
Poststack seismic data are sensitive to the variations in: a. P-wave velocity b. S-wave velocity c. Density d. P-wave impedance (P-wave velocity times density) e. S-wave impedance (S-wave velocity times density)
P-wave impedance (P-wave velocity times density)
Why do you think the prestack waveform inversion (PWI) provide much superior subsurface model compared to poststack or amplitude-variation with offset inversion? a. PWI takes much longer time to run than the other two, so it better be good. b. PWI uses complex effects of wave propagation into its algorithm and the other two methods are based on simplified physics. Consequently, PWI produces superior results than the other two. c. PWI needs a parallel computer to run but the other two methods do not.
PWI uses complex effects of wave propagation into its algorithm and the other two methods are based on simplified physics. Consequently, PWI produces superior results than the other two.
Neutron logs are sensitive to: a. Formation radioactivity b. Water saturation c. Porosity d. Seismic velocity e. Density
Porosity
Gravity methods of geophysical exploration could be effective in delineating a. Structural traps only b. Stratigraphic traps only c. Structural, stratigraphic, and possibly other types of traps
Structural, stratigraphic, and possibly other types of traps
In the fluid substitution equations, what is the physical explanation of the fact that the rigidity modulus of the fluid-saturated rock is equal to that of the dry rock? a. Rigidity modulus of the rock matrix and that of fluids is about same such that the shear waves propagate at the same speed through the rock matrix and through the pore fluids. b. Rigidity modulus of the fluids is zero and the shear waves do not propagate through the pores and they propagate only through the rock matrix.
Rigidity modulus of the fluids is zero and the shear waves do not propagate through the pores and they propagate only through the rock matrix.
In the normal process of burial and compaction sediments, as water moves upward through compacting sediments, the shale prevents the salt ions from escaping from the sand. The net result is a general increase of salinity with depth. This phenomenon is called a. Salt filtering b. Salt sieving c. Salt capture d. Osmosis
Salt sieving
The most effective geophysical method in petroleum exploration is a. Gravity b. Electromagnetic c. Seismic d. Magnetic e. Electrical Resistivity
Seismic
In fluid substitutions when you substitute a 100% brine saturated rock to 100% gas, the shear wave velocity (Vs) will a. Drastically increase b. Stay about the same or slightly increase c. Drastically increase d. Slightly decrease
Stay about the same or slightly increase
What is the difference between the bulk modulus of the dry rock (Kdry) and that of the frame (Ko) used in the fluid substitution equation? a. They are exactly the same. b. They are not the same, but approximately equal for all practical purposes. c. The frame bulk modulus (Ko) is the average bulk modulus of the minerals that constitute the solid part of the rock while the dry rock bulk modulus (Kdry) is the bulk modulus of the rock where all its pores are empty.
The frame bulk modulus (Ko) is the average bulk modulus of the minerals that constitute the solid part of the rock while the dry rock bulk modulus (Kdry) is the bulk modulus of the rock where all its pores are empty.
Distribution of the gas hydrate in the world oceans suggest that it could be a potential source of energy in the future. a. True b. False
True
Due to high thermal conductivity, the isotherms usually dome up above the salt diapirs and are depressed below them: a. True b. False
True
During the first millennium AD, primary use of oil was medication, waterproofing, and warfare. a. True b. False
True
Consider reflection between a shale layer on top with a Poisson's ratio of .35 and a gas sand layer below with a Poisson's ratio of .1. For simplicity, also assume that the P and S-wave velocity (Vp and Vs) and density (p) are exactly the same for both sand and shale. How would you expect the reflection coefficient to vary with the incidence angle? a. Will be positive at zero degree and increase as the incidence angle increases. b. Will be negative at zero degree and decrease with increasing incidence angle. c. Will be zero at zero degree and remain constant as the angle of incidence increases. d. Will be zero at zero degree and keep decreasing as the angle of incidence decreases.
Will be zero at zero degree and keep decreasing as the angle of incidence decreases.
Can porosity be calculated from the density and sonic logs? a. Yes b. No
Yes
Does areas of high salinity from the regional isohaline maps indicate possibility of rich oil/gas accumulations? a. Yes b. No
Yes
Does the geothermal gradient depend upon the subsurface lithology? a. Yes b. No
Yes
With reference to the previous question (question 39), do you expect the sandstones beneath the salt diapirs to be more porous than their lateral equivalents at similar depths but not situated below the salt diaper? a. Yes b. No
Yes
