Geophysics 559-University of Calgary

Geophysics 559-Geophysical Interpretation

In class midterm will be mostly multiple choice; but there will be also written questions.

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Geophysics 559 (GOPH 559) Midterm

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Question 1

Given the gravitational attraction of a Bouguer slab (a layer) by 2πGρt, where G is the universal gravitational constant, ρ is the slab density and t is the thickness. The gravity meter that pass from top to the bottom layer will result in what type of reading? (ID-GIM-23)

A	It will be a reduced reading by a factor of 2πGρt.
B	It will be a reduced reading by a factor of 4πGρt.
C	It will be a increased reading by a factor of 4πGρt.
D	It will be a increased reading by a factor of 2πGρt.

Question 2

If a bottom of a reservoir containing oil, water and gas begins to leak due to permeability increase in the bottom sea, what fluid would most likely to drain first? (ID-GIM-18)

A	Water
B	Cannot be answered with the given information.
C	Oil
D	Gas

Question 2 Explanation:

This is a practical question. Since all three fluid types are present, the densities dictate which fluid will be stable as depth increase. Hence, gas-oil-water from top to bottom. If the bottom seal leaks, the first fluid to escape is water.

Question 3

What is the best probable seismic velocity for tight limestone? (ID-GIM-03)

A	6000 m/s
B	1500 m/s
C	4000 m/s
D	10 m/s
E	200 m/s

Question 3 Explanation:

You should have a general idea about what velocities to expect from each layer!

Question 4

Measurements made in a mountainous terrain would give ___ gravity readings. (ID-GIM-06)

A	high
B	Not enough information to answer the question.
C	low

Question 5

In reflection seismology, the velocity is estimated using what technique? (ID-GIM-28)

A	Reciprocity
B	Convolution
C	Deconvolution
D	Normal Moveout

Question 6

What is the best temperature range for petroleum source rocks? (ID-GIM-09)

A	0 - 200 degree Celsius
B	50 - 150 degree Celsius
C	20 - 200 degree Celsius
D	250 - 350 degree Celsius
E	200 - 350 degree Celsius

Question 7

You obtained a seismic profile and core samples for an area of interest. The core samples indicate that the lithology in the area is the same. However, the seismic profile shows lower velocities in some localized regions. What is most likely the cause for this anomaly? (ID-GIM-04)

A	Change in lithology.
B	Change in density.
C	Fractures within the formation.
D	Change in dip angles.

Question 7 Explanation:

Change in density is also a possible answer. But the best answer is fractures within the formation. If there is a large density change then the lithology must have been changed too. However, the core samples shows that the lithology is the same.

Question 8

Which of the following seismic method is most sensitive to variation in physical properties of lithology? (ID-GIM-32)

A	Seismic interference
B	Gravity survey
C	Magnetic survey
D	None of the above
E	Acoustic impedance

Question 9

What is the zero length spring? (ID-GIM-20)

A	A spring that is under maximum tension (maximum stretch).
B	A theoretical name given to springs that obey its spring constant, k.
C	A spring that has no length but only diameter.
D	A theoretical name given to springs that do not obey its spring constant, k.
E	A theoretical name given to springs that are not being stretch.

Question 10

Electrical and electromagnetic surveys are typical used for measuring what type of physical properties? (ID-GIM-21)

A	Oil and gas exploration
B	Mineral exploration
C	Hydrological research (drinking water, fresh water)
D	Identification of basement features

Question 11

Poisson's relation is between what type of energy, forces or concepts? (ID-GIM-07)

A	Gravitational and Potential energy
B	Incident and Refractory rays
C	Gravitational and Magnetic forces
D	Spring Constant and magnitude of gravity

Question 12

Which of the following will result in aliasing? (ID-GIM-29)

A	Increase in seismic frequency.
B	Having a frequency below the Nyquist value.
C	Increasing spatial sampling.
D	Decrease in period.

Question 13

You randomly weighed an item in several different locations on Earth, at which location would you expect the record the highest weight reading? (ID-GIM-19)

A	The location closest to the poles.
B	The location with the highest elevation and the lowest latitude.
C	The location with the lowest elevation and the highest latitude.
D	The location closest to the equator.
E	The location between the equator and the poles (middle).

Question 14

In seismic signal processing, coherency can be best described as a function of... (ID-GIM-31)

A	...time (and time only).
B	...frequency (and frequency only).
C	...similarities between seismic events.
D	...wavelength (and wavelength only).

Question 15

What is an another tern used to describe a head wave in reflection seismology? (ID-GIM-26)

A	Guided wave
B	Direct wave
C	Critically refracted arrival
D	Transmitted wave
E	Refracted arrival

Question 16

What is the primary factor driving the hydrocarbon migration from structurally low to structurally high regions? (ID-GIM-11)

A	Buoyancy
B	Pressure
C	Porosity
D	Temperature
E	Gravity

Question 17

You are a fracking expert. In which direction would you expect to have the highest permeability in a fracked region? (ID-GIM-13)

A	It depends on the rock type and the formation.
B	Across or perpendicular to fractures.
C	Along any angle between the fractures and natural permeability pathways.
D	Along the plane of the fractures.

Question 17 Explanation:

The whole point of fracking is to increase the permeability which occurs along the fractures.

Question 18

Which of the following will result in a high gravity reading? (ID-GIM-05)

A	Slab and Terrain effects
B	Latitude and Slab effects
C	Free Air and Slab effects
D	Free Air and Terrain effects
E	Latitude and Free Air effects

Question 19

Rays travel in paths that would take the least amount of time. This law/principle is known as... (ID-GIM-22)

A	Principle of Reciprocity
B	Fermat's Principle
C	Refraction Law
D	Snell's Law

Question 20

A tight reservoir would have a permeability of ___ millidarcys (md). (ID-GIM-12)

A	less than 5
B	greater than 10
C	greater than 30
D	greater than 50
E	less than 40

Question 21

The peak oil generation occurs at what temperature? (ID-GIM-10)

A	200 degree Celsius
B	90 degree Celsius
C	70 degree Celsius
D	150 degree Celsius
E	50 degree Celsius

Question 22

What does a seismic geophone detect or measure? (ID-GIM-01)

A	Depth of reflectors
B	Speed or velocity
C	Density of formations
D	Vibrations

Question 23

Which of the following is situated at the highest temperature / depth? (ID-GIM-17)

A	Oil floor
B	Dry gas preservation limit
C	Wet gas preservation limit
D	Oil window

Question 24

Areal survey is a relatively cheap method of seismic data acquisition. This type of surveys have been used for over, (ID-GIM-25)

A	150 years.
B	20 years.
C	50 years.
D	100 years.

Question 25

Which of the following is the best description for a hydrocarbon trap? (ID-GIM-08)

A	A body of rock that is capable of containing hydrocarbons due to perfectly impermeable barrier.
B	A Geologic area that is capable of containing hydrocarbons due to relatively impermeable barrier.
C	A highly conductive (high effective porosity) stratigraphic or a rock body that is capable of containing hydrocarbon.
D	A specific area of a specific Formation in which the temperature is between 50 - 150 degree Celsius.

Question 25 Explanation:

You may have found more than one answer possible for this question. You are WRONG; please study harder. 😉

Question 26

The normal moveout deal with the... (ID-GIM-24)

A	reduction of seismic resolution as a result of smaller variation in densities of different layers and the depth to the reflection surface.
B	effect that the distance between a seismic source and a receiver (the offset) has on the arrival time of a reflection.
C	density contrast between two layers adjacent to each other.
D	resolution of layers with extremely small difference in densities.

Question 27

Given a sampling interval of 3ms, calculate it's Nyquest frequency. (ID-GIM-30)

A	255.8 hz
B	166.7 Hz
C	512.2 Hz
D	322.9 Hz

Question 27 Explanation:

F_N = 1/2t

Question 28

Which of the following best describe a real world scenario? (ID-GIM-02)

A	A very good reservoir with 100% pure oil and no impurities or other type of fluids.
B	A very good reservoir with no significant traps.
C	Gas at the very top of the reservoir followed by oil and water as the depth increases.
D	Oil at the very top of the reservoir followed by gas and water as the depth increases.

Question 29

Which of the following type of rock/lithology has the highest density? (ID-GIM-16)

A	Sandstone
B	Limestone
C	Salt
D	Igneous rocks
E	Shale

Question 30

Which of the following statement is true? (ID-GIM-27)

A	The head wave travels further than the direct wave, but it has a higher velocity.
B	The head wave only travels in the first medium.
C	The direct wave has a sinusoidal wave form while the head wave does not.
D	The direct wave travels faster than the head wave.

Question 31

Which of the following is a stratigraphic trap? (ID-GIM-14)

A	Foliations
B	Reefs
C	Folds
D	Faults

Question 32

Which of the following is the best method to interpret the processes of source-rock deposition? (ID-GIM-15)

A	Comprehensive understanding of the regional Geology.
B	Density measurements obtained through seismic data.
C	2D and 3D structural modeling of the area.
D	Advanced well-logging data obtained through a combination of core samples and seismic data.

Question 32 Explanation:

You may found that more than one answer is possible. You are WRONG; only one answer is correct.

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Credits: Based on the excellent class notes provided by, Dr. Laurence Lines during Winter 2015.
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Given the faulted slab equation, , prove that the edge of the buried slab occurs at the inflection point of the gravitational profile curve.

Sanuja Senanayake

Geophysics 559-University of Calgary

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Geophysics 559 (GOPH 559) Midterm

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Standing on the shoulders of giants