Introduction to Petroleum Geology

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Geology (GLGY 577-UCAL) Midterm Exam

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Question 1

Neutron porosity, ΦN is measured to be 15% and the Density porosity, ΦD is measured to be 10% on a sandstone calibrated matrix. It is plotted on the Schlumberger CP-1e as shown below (red circles). What is the true porosity given there is no gas effect in this particular section? (ID-PGL-53)

A	15%
B	12%
C	6%
D	5%
E	10%

Question 2

How would you obtain Rw and So maximum from a Pickett Plot? You may use the following diagram to answer this question. (ID-PGL-57)

A	So maximum is the intersect point between the lower boundary (green line above) and read off the x-values straight down (first brown dash line down). The Rw is the x-value of the upper most point and read off the x-axis (second brown dash line).
B	Rw is obtained from the upper limit of the lower boundary (red line above) and So maximum is obtained from the upper boundary (green line above).
C	Rw is the intersect point between the lower boundary (green line above) and read off the x-values straight down (first brown dash line down). The So maximum is the x-value of the upper most point and read off the x-axis (second brown dash line).
D	Rw is obtained from the upper boundary (green line above) and the Sw is obtained from the upper limit of the lower boundary (red line above).
E	You cannot take these measurements from a Pickett Plot. You must use a well log to determine such properties.

Question 3

Typically, what is the resolution thickness of deep dual induction tools (ILd)? (ID-PGL-29)

A	~ 80 cm
B	~ 1.5 m
C	~ 3 m
D	~ 50 cm
E	~ 2.5 m

Question 4

Calculate the sand:shale for the interval between 1000 m and 5000 m on the following Gamma Ray (GR) curve. Assume a sand cut-off of 75 API. (ID-PGL-56)

A	~ 0.20
B	~ 3.50
C	~ 2.81
D	~ 0.71
E	~ 1.76

Question 4 Explanation: 

Net sand interval = 3550 m - 1000 m = 2550 m (read off the GR curve)
Net shale interval = 5000 m - 3550 m = 1450 m (read off the GR curve)
Hence, sand:shale = 2550 m/1450 m = 1.7586...

Question 5

Typically what would you expect to observe on shale conductivity? (ID-PGL-32)

A	Decrease with increase in hydrocarbon saturation.
B	Decrease with increase in clay interbedding.
C	Becomes almost zero with hydrocarbon saturation.
D	Decrease with depth.
E	Increase with sand interbedding.

Question 6

Which of the following statement is true about fromation factor, F? (ID-PGL-23)

A	Porosity and formation factor is directly related to each other.
B	Formation factor is inversly related to tourtousity factor.
C	Pore stucture is directly related to the formation factor.
D	Clean granular formations have a lower formation factor than clean carbonate formations.

Question 7

Calculate Sw using the data obtained from following interpreted Pickett Plot. (ID-PGL-58)

A	0.08
B	0.65
C	1.00
D	1.08
E	0.09

Question 7 Explanation: 

Sw = (Ro/Rt)^(1/2) = (0.6/70)^(1/2) = 0.09258....

Question 8

Given following information, calculate Net:Gross and Sand:Shale values. (ID-PGL-41)
net sand = 15.5 m
shale = 5.3 m
gross thickness = 26.3 m

A	Net:Gross = 0.59 and Sand:Shale = 2.92
B	Net:Gross = 0.59 and Sand:Shale = 0.34
C	Net:Gross = 0.79 and Sand:Shale = 0.34
D	Net:Gross = 59 and Sand:Shale = 29
E	Net:Gross = 59 and Sand:Shale = 34

Question 8 Explanation: 

On the exam you will most likely be given a well log. You will have to calculate the above given values from the log. You should know how to read logs.

Question 9

Regardless of the scale, what can you derive from the following gamma ray (GR) signature? (ID-PGL-49)

A	Coarsening downward sequence
B	Very high gamma ray kick Hint: You need the scale for this interpretation.
C	Net sand content Hint: You need the scale for this calculation.
D	Coarsening upward sequence

Question 10

What is the primary purpose of steam injection into a zone of crude oil? (ID-PGL-09)

A	Decrease friction between the pore walls and the crude oil.
B	Increase pressure within the chamber hence driving the crude oil out of the system.
C	Increase pressure within the chamber which facilitate extraction.
D	It will reduce viscosity of crude oil hence allowing it to be pumped.
E	Increase the conductivity between pores.

Question 11

As a Petroleum Geologist, you often have to make decisions based on limited access to samples and data. Your boss sent you the following image of a core from an unknown location at an unknown depth. Just by looking at the image, which of the following statements would you submit to your boss? (ID-PGL-34)

A	This part of the core is most likely saturated with organic materials.
B	This part of the core is most likely harder and stronger relative to other areas of the core.
C	This part of the core is most likely saturated with hydrocarbons.
D	This part of the core is most likely have a very high permeability.
E	This part of the core is most likely concentrated with bitumen.
F	This part of the core is most likely have a very low permeability.

Question 11 Explanation: 

For this question, multiple answers are possible. You may choose the one with bitumen and hydrocarbons and argue that those answers are correct. However, on multiple choice exams you are expected to choose most suitable answer. Technically you cannot say this is hydrocarbons (HC) or bitumen because by definition, you must satisfy the chemical and physical properties of such materials in order to classify as such. But the term "organic materials" can be used for border range of things including HC and bitumen.

Question 12

Fossil fuels are chains of... (ID-PGL-01)

A	transitional metals and carbons.
B	carbon-oxygen bonds.
C	inorganic compounds.
D	kerogen.
E	carbon-hydrogen bonds.

Question 13

Which of the following environment would you expect to find most trace fossils? (ID-PGL-40)

A	Deep marine
B	Point bars
C	Beach marine
D	Tidal flats

Question 14

Which of the following combination most likely result in formation of crude oil during diagenesis? (ID-PGL-02)

A	Carbohydrates and Proteins
B	Proteins and Lignin
C	Carbohydrates, Proteins and Lipids
D	Lignin, Carbohydrates, Proteins and Lipids
E	Proteins and Lipids
F	Lignin and Carbohydrates

Question 15

If you have multiple possibilities for the line of Ro on the Pickett Plot, what is the best approach for obtaining Sw? (ID-PGL-25)

A	Generate several Ro lines on the Pickett Plot.
B	Generate several parallel Ro lines on the Pickett Plot.
C	Calibrate the Ro line with the core or well logs.
D	Generate the most two extreme Ro lines on the Pickett Plot with the maximum Rt and minimum Rt as your reference bounds.
E	Use the Ro line that is most centered to the all other Ro lines.

Question 16

The F factor becomes extremely difficult to obtain when... (ID-PGL-26)

A	...the formation is saturated with fresh water.
B	...the formation is concentrated with clay minerals in saline waters.
C	...the formation is low in clay minerals.
D	...the formation is composed of highly complex pore structures.

Question 17

Generally what is the reference elevation for core samples taken out of a drilling operation? (ID-PGL-11)

A	Position of the Kelly Bushing
B	Lowest point of the hydrocarbon pool
C	Highest point of the hydrocarbon pool
D	Top of the major formation
E	Bottom of the major formation

Question 18

Which of the following is true about cementation factor, m? (ID-PGL-24)

A	All or other things being equal, increase in m will result in decrease in a.
B	The m and porosity are directly related to each other.
C	Value of m is independent of the surface area of the pores.
D	All or other things being equal, as m increases, the prore geometry become complicated.
E	All or other things being equal, increase in m will result in increase in formation factor, F.

Question 19

Ideal diagenesis of organic matter will result in... (ID-PGL-04)

A	traps.
B	kerogen.
C	carbon-oxygen chains.
D	reservoir.
E	hydrocarbons.

Question 20

Fining upwards sequence is associated with which of the depositional history? (ID-PGL-54)

A	Progradating marine shelf
B	Fluvial point bar deposits
C	Progradating delta deposits
D	Deep marine sediments

Question 21

Which of the following is the most problematic issue with picking a wrong datum? (ID-PGL-51)

A	The calculated net sand volume may be incorrect.
B	The overall assessment of the geology may be completely wrong.
C	The key well logs features may not be able to correlate further away from the reference wells.
D	The obvious features of the well logs may be ignored.
E	The topography of the area may be distorted.

Question 22

Which of the following geophysical data is cheapest to run? (ID-PGL-50)

A	2D seismic data acquisition
B	3D seismic data acquisition
C	Crosswell seismic data acquisition
D	4D seismic data acquisition

Question 23

What is tight gas? (ID-PGL-10)

A	Natural gas produced from reservoir rocks with such low permeability that massive hydraulic fracturing is necessary to produce the well at economic rates.
B	Natural gas produced from reservoirs after the peak production of the play. In other words, low yield gas produced after production has been in place for a period of time.
C	Natural gas produced from reservoirs that are under very high pressures making it tight and easier to extract.
D	Natural gas produced from reservoir rocks that are interbeded with alternating permeable and non-permeable layers.

Question 24

As resistivity ____ the conductivity ____. Answers are in respective order. (ID-PGL-19)

A	They are not related to each other.
B	decarses , decrease
C	increases , decrease
D	increase , increase

Question 25

Given C_H = 0.102 what is the R_H? (ID-PGL-20)

A	102.0 Ωm
B	120.0 Ωm
C	9.80 Ωm
D	0.102 Ωm

Question 25 Explanation: 

R_H = 1/C_H

Question 26

What is the difference between a play and a prospect? (ID-PGL-08)

A	The play is an area of interest for petroleum exploration while the prospect is an area within a play that is expected to produce hydrocarbons.
B	The play is an area where common petroleum system characteristics exists, while the prospect is an area where the hydrocarbons can be extracted economically.
C	The play is an area of interest for petroleum exploration and a prospect is the lowest point on the trap which can hold petroleum.
D	The play is a large area where hydrocarbons may be found, while the prospect is an area where there is a current production in hydrocarbons.
E	None of these answers are correct.

Question 27

Calculate the net:gross for the interval between 1000m and 5000m on the following Gamma Ray (GR) curve. Assume a sand cut-off of 75 API. (ID-PGL-55)

A	~ 4.00
B	~ 0.20
C	None of the answers are correct.
D	~ 3.50
E	~ 0.64

Question 27 Explanation: 

Gross thickness = 5000 m - 1000 m = 4000 m
Net sand interval = 3550 m - 1000 m = 2550 m (read off the GR curve)
Hence, net:gross = 2550 m/4000 m = 0.6375

Question 28

Which of the following provide the best analytical evidence for specific formation properties (eg. type of rock, porosity, etc)? (ID-PGL-13)

A	Core samples
B	Wireline well logs
C	Seismic sections
D	Geostatistical models such as kriging
E	Gravity readings

Question 29

Typically, what is the depth of investigation for deep induction tools (ILd)? (ID-PGL-30)

A	0.5 - 1.5 m
B	0.5 - 2m
C	1 - 5 m
D	2 - 3 m
E	0.8 - 1.5 m

Question 30

The following is a map section created using the Canadian Dominion Land Survey (DLS) method. What is the location number for the X position? (ID-PGL-43)

A	Section 5
B	Section 4
C	Section 9
D	Section 10
E	Section 3

Question 31

Which of the following drilling mud has the lowest impact on the environment? (ID-PGL-12)

A	Acids-based mud
B	Synthetic mud
C	Oil-based mud
D	Denial-based mud

Question 32

Which of the following has the best verticale resolution? (ID-PGL-47)

A	Gamma ray log
B	Dipmeter log
C	Neuron log
D	Caliper log
E	Sonic log

Question 33

Typically which data source would provide the largest area coverage? (ID-PGL-46)

A	4C seismic
B	2D seismic
C	3D seismic
D	4D seismic

Question 34

Knowing that it is a stratigraphic trap, what is represented by diagram E? (ID-PGL-06)

A	Salt dome trap
B	Lens trap
C	Fault trap
D	Anticline trap
E	Unconformity trap
F	Pinchout trap

Question 35

The best resistivity data used for identification of lithology are obtained from which of the following? (ID-PGL-27)

A	Rw
B	Rm
C	Rmc
D	Rt
E	Ro

Question 36

What is the depth of investigation for the deep lateral resistivity log? (ID-PGL-17)

A	~ 26 to 30 cm
B	~30 to 50 cm
C	~ 1.35 to 1.75 m
D	~ 1.2 to 1.25 m
E	~ 1.1 to 2 m

Question 37

Which of the following is true (scientifically) regrading fracking? (ID-PGL-37)

A	It will not affect aquifers.
B	It may result in earthquakes.
C	It is a relatively very new technology.
D	It is easier to frack on soft sediments.

Question 38

At what stage during the natural formation of crude oil the cracking take place? (ID-PGL-03)

A	Initial burial
B	Diagenesis
C	Zone of gas formation
D	Catagenesis
E	Unaltered organic matter

Question 39

Typically when interpreting wireline well logs, the sand zones will produce _____ Gamma Ray (GR) readings, shale zones will produce _____ Gamma Ray (GR) readings and the threshold value for differentiating between sand and shale is ___. (ID-PGL-14)

A	high , low , arbitrary
B	high , low , at 75 API
C	high , low , at 15 API
D	low , high , arbitrary
E	low , high , at 15 API
F	low , high , at 75 API

Question 40

On the following hypothetical geologic map, the black lines are strike lines. When drawing cross sections, the line in _____ can be used as a dip section plane, the line in _____ can be used as a strike section plane, and the line in ____ can be used as an oblique section plane. Answers are in respective order. (ID-PGL-52)

A	blue , orange , green
B	orange , green , blue
C	green , orange , blue
D	orange , blue , green
E	blue , green , orange
F	green , blue , orange

Question 41

What is the first step in petroleum systems "value chain"? (ID-PGL-07)

A	Development
B	Reserves Growth
C	Exploration
D	Production
E	Appraisal

Question 41 Explanation: 

This is supposed to be an easy question.

Question 42

In order to correct the depth measurements of cores obtained from diverted or horizontal wells, you must obtain which of the following? (ID-PGL-35)

A	Total length of the recovered core.
B	Porosity and permeability of the core.
C	Length of the drill string.
D	Well diversion trajectory angles.

Question 43

The Caesium-137 is commonly used as the source for which of the following well logging tools? (ID-PGL-39)

A	Gamma Ray tools
B	Neutron tools
C	Resistivity tools
D	Density tools

Question 44

Calculate the geothermal gradient given following information. (ID-PGL-33)
BHT (bottom hole temperature) = 255^o F
Surface temperature = 75^o F
Depth which BHT was measured: 11400 ft

A	~ 0.018oF/ft
B	~ 0.029oF/ft
C	~ 0.028oF/ft
D	~ 0.016oF/ft
E	~ 0.015oF/ft

Question 44 Explanation: 

Usually on exams, you will be required to read some of the values from a wireline well log.

Question 45

Typically, what is the vertical resolution of Gamma Ray logs? (ID-PGL-38)

A	~ 80 cm
B	~ 40 cm
C	~ 10 cm
D	~ 30 cm

Question 46

Which of the following is not an assumption used in Archie equation? (ID-PGL-22)

A	Oil and gas acts as conduits for electrical signals.
B	Formation is completely saturacted with fulids.
C	Resistivity of the formation water is same above and below the contact.
D	Proposity must be the same both above and below the oil-water contect.
E	Formation must be clean and free of clay.

Question 47

Why would you choose metal casings as opposed to mud casings for top sections of the wells? (ID-PGL-36)

A	To provide support for the Kelly Bushing.
B	To protect aquifers from contamination.
C	To reduce fractures near the neck.
D	To prevent well blowouts.

Question 47 Explanation: 

Usually aquifers are situated close to the surface (relative to the deepest part of the well). Hence using mud may result in cross contamination.

Question 48

Which of the following fraction has the highest number of carbons per molecule (highest boiling point)? (ID-PGL-05)

A	Diesel fuel
B	Kerosene
C	Residuum
D	Lubricating oil
E	Heavy gas oil
F	Gasoline

Question 49

Seimic data are difficult to obtain when.... (ID-PGL-48)

A	there are multiple sleeply dippinng beds.
B	the seismic signals have to travel through fluids (eg. oceanic seismic).
C	the beds has no dip, hence almost horizontal.
D	the beds are extremly thick.

Question 50

Which of the following condition would increase the invasion of drilling mud filtrate? (ID-PGL-45)

A	Very high permeability in the formation.
B	Very low formation pressures.
C	Very high porosity in the formation.
D	Very high formation pressures.

Question 51

Thin areas on isopach maps are indicative of which of the following characteristic? (ID-PGL-42)

A	High net pay regions
B	High concentration of hydrocarbons
C	Hills or mountains
D	Valleys
E	Low net pay regions

Question 52

Which of the following statement is true about the neutron wireline tool? (ID-PGL-15)

A	The thermal phase of the tool uses energy at around 10 eV
B	Typically, silicon has a higher neutron reading than carbon.
C	It measures the true density of the material.
D	A typical tool uses uranium as the energy source.
E	It measures the slow-down length of neutrons when they interacts with atoms.

Question 53

Which of the following frequency can be used in conduction resistivity measurements? (ID-PGL-21)

A	20 MHz
B	2 kHz
C	2 MHz
D	200 Hz
E	100 kHz

Question 54

Which of the following formation factor most likley represent a rock that contains almost all fuild? (ID-PGL-18)

A	F = 0.2
B	F = 0.5
C	F = 2.2
D	F = 0.7
E	F = 0.9

Question 55

Tortuosity factor... (ID-PGL-31)

A	is directly proportional to the resistivity.
B	is highly dependent on the formation factor.
C	varies between 0.35 and 4.5.
D	is most commonly found to be equals to 1.0.

Question 56

Which of the following property would adversely effect measurements and operation of well logging tool? (ID-PGL-28)

A	High concentration of formation fluids.
B	Low viscosity mud.
C	Directionally focused tools.
D	Low mud invasion zone.

Question 56 Explanation: 

Low viscosity mud have two major problems. It may not be able to counteract the formation pressures. Secondly, it will most likely penetrate deep into the formation where formation pressures is too low. Most drilling mud are neither high viscous nor low viscous.

Question 57

Most neutron tools use which of the following? (ID-PGL-16)

A	Uranium source
B	Electric energy
C	Thermal phase of the scatter
D	Epi-thermal phase of the scatter

Question 58

Which of the following is true? (ID-PGL-44)

A	Typically, as you move closer to mountains, frequency of structural traps increases.
B	Computer algorithms for reservoir characterization models heavily depends on the analytical variables as opposed to empirical variables.
C	In Alberta, we commonly find oil-wet rocks in the subsurface.
D	In Alberta, lens traps are the most common type of hydrocarbon traps.
E	Typically, as you move closer to mountains, frequency of stratigraphic traps increases.

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