Module 9.Reservoir Geology

Question 1

Name types of Geophysical surveys

Answer 1

Aeromagnetic and marine magnetic surveys
Gravity surveys (onshore and offshore)
Refraction and relection seismic surveys

Question 2

What is a VSP?

Answer 2

A vertical seismic profile - closely spaced down-hole geophones record “check-spots” from a surface energy source, enabling the identification of down-hole seismic reflectors

Question 3

Explain 4-D surveys

Answer 3

the fourth dimension , time, is added by shooting both 3-D seismic and VSP surveys at regular intervals during the lifetime of a producing field (this enables monitoring of fluid movement)

Question 4

Name three sub-surface exploration methods

Answer 4

Drilling and Completion
Formation Evaluation
Subsurface geology

Question 5

Why is a DST done?

Answer 5

to isolate and test permeability , pressure, and productive capacity of a res (done while drilling the well)

Question 6

Two types of Geological cross-sections

Answer 6

Stratigraphic and structural

Question 7

Name three types of subsurface geological maps

Answer 7

Facies maps
Structural contour maps
isopach maps

Question 8

What is palynology

Answer 8

looks at fossilized spores and pollen for age-dating and correlation

Question 9

what is micro-paleontology?

Answer 9

Looks at fossils for age-dating and correlation

Question 10

What is geochemistry?

Answer 10

Looks at source rocks and oil typing

Question 11

What is basin analysis?

Answer 11

Looks at structural, stratigraphic, reservoir, geochemical, resource estimation

Question 12

Petroleum seismic surveying is more concerned with refracted or reflected ray paths?

Answer 12

Reflected

Question 13

What are some applications of reflection seismic surveys?

Answer 13

Onshore : vibroseis energy source, geophones , recoring truck
Offshore: ship-based energy source (air guns), marine streamer (geophones), recorded onborad

Question 14

What does a geophysical gravity survey measure??

What does it mean when there is an Excess and a Deficiency?

Answer 14

It measures rock density
Excess observed gravity produces a positive anomaly (high)
A deficiency produces a negative anomaly (low)

Question 15

What does a geophysical magnetic survey measure?

Answer 15

It measures magnetic susceptability

Question 16

What does a geophysical seismic survey measure?

Answer 16

It measures the time of acoustic wave transmission

Question 17

Why does the gravitational acceleration on the Earth’s surface vary? 4 Factors

Answer 17

Latitude, Elevation, Topography, Geology

Question 18

What is a correction(s) (in relation to the varying gravitational acceleration)

Answer 18

Understanding that the 4 varying factors require changes.
Latitude - earth is not a true sphere
Elevation - Gravity decreases with increased elevation
Topography - The mass of rock between the survey and reference datum changes

Question 19

The Bouguer anomaly is what? explain what is required for it to happen and the resulting units

Answer 19

It’s the resultant value of the gravitational acceleration after corrections have been made
The unit of, a, is in gals - where 1 gal is an acceleration of 1cm/s^2

Question 20

What is the application of a gravity map?

Answer 20

useful for showing the broad architecture of a sedimentary basin

Question 21

When trying to locate salt domes and reefs VIA gravity maps what should you look for?

Answer 21

Salt = low gravity b/c extremely low density

Coral reef = high gravity b/c higher density

Question 22

What’s the magnetic field strength at the poles vs the equator?

Answer 22

60,000 gamma (0.6 oersted) vs. 35,000 (0.35 oersted)

Question 23

What is the purpose of a magnetic survey?

Answer 23

measure the field strength

Question 24

Corrections done in magnetic survey remove what?

Answer 24

Changes in the Earth’s magnetic field

Question 25

What three categories can open hole logs be placed into?

Answer 25

Natural Detection (SP, Gamma Ray)
Porosity (Sonic. Density, Neutron)
Resistivity (E-logs, Introduction, Laterologs)

Question 26

What are the uses of well logs?

Answer 26

Determination of lithology
Evaluation of zones
Correlation of zones

Question 27

What are the uses of well logs?

Answer 27

Determination of lithology
Evaluation of zones
Correlation of zones

Question 28

What data can you measure from a core?

Answer 28

Porosity
Permeability
Oil and Water saturations (in 3 directions)
Grain density

Question 29

Name 5 duties of the geologist

Answer 29

Monitors progress of well for head office
Pick up casing and core points
Develop logging program
Supervise logging and interpret results
Identify shows in the well (using ultraviolet light)

Question 30

What do mud loggers record?

Answer 30

rate of penetration
mud temperature
Pore pressure
Shale density

Question 31

What monitors the presence of hydrocarbons in gas wells?

Answer 31

Gas chromatographs

Question 32

Why is the rate of penetration a good indicator of the rock type and porosity?

Answer 32

Lithologies like chert and anhydrite drill more slowly,, depending on drillbit. Porous rock drill faster than tight rocks, and shallow formations tend to drill faster as they are usually less lithified and therefore softer. A speed up in ROP usually indicated a softer lithology.

Question 33

What 2 tests measure formation fluids and reservoir pressure?

Answer 33

Drillstem tests and repeat formation tests

Question 34

Are DST’s open to surface?

Answer 34

YES

Question 35

RFT’s are run on a wireline. Do they have open or closed sample chambers?

Answer 35

CLOSED

Question 36

What 5 things are considerations of a good geologic prospect?

Answer 36

Good geologic factors
Good economics
Accessibility
Subsurface rights
Company risk profile

Question 37

What 5 things should be included when compiling a geologic prospect?

Answer 37

Data collection
Data manipulation
Data interpretation
The prospect map
Selling the prospect