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

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

Question 1 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 2

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

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

Question 3

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

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

Question 3 Explanation:

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

Question 4

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 5

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

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

Question 6

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

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

Question 7

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

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

Question 8

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

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

Question 9

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

A	Convolution
B	Reciprocity
C	Normal Moveout
D	Deconvolution

Question 10

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

Question 11

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 specific area of a specific Formation in which the temperature is between 50 - 150 degree Celsius.
D	A highly conductive (high effective porosity) stratigraphic or a rock body that is capable of containing hydrocarbon.

Question 11 Explanation:

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

Question 12

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

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

Question 13

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

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

Question 14

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

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

Question 15

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

A	Faults
B	Foliations
C	Reefs
D	Folds

Question 16

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

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

Question 16 Explanation:

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

Question 17

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

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

Question 17 Explanation:

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

Question 18

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

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

Question 19

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

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

Question 20

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

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

Question 21

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

Question 21 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 22

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

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

Question 23

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	resolution of layers with extremely small difference in densities.
D	density contrast between two layers adjacent to each other.

Question 24

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

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

Question 24 Explanation:

F_N = 1/2t

Question 25

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

A	Shale
B	Sandstone
C	Igneous rocks
D	Salt
E	Limestone

Question 26

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

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

Question 27

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

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

Question 28

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

A	Temperature
B	Buoyancy
C	Porosity
D	Pressure
E	Gravity

Question 29

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

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

Question 30

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

Question 31

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

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

Question 32

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

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

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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

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Geophysics 559 (GOPH 559) Midterm

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Standing on the shoulders of giants