Module 9.Reservoir Geology Flashcards
Name types of Geophysical surveys
Aeromagnetic and marine magnetic surveys
Gravity surveys (onshore and offshore)
Refraction and relection seismic surveys
What is a VSP?
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
Explain 4-D surveys
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)
Name three sub-surface exploration methods
Drilling and Completion
Formation Evaluation
Subsurface geology
Why is a DST done?
to isolate and test permeability , pressure, and productive capacity of a res (done while drilling the well)
Two types of Geological cross-sections
Stratigraphic and structural
Name three types of subsurface geological maps
Facies maps
Structural contour maps
isopach maps
What is palynology
looks at fossilized spores and pollen for age-dating and correlation
what is micro-paleontology?
Looks at fossils for age-dating and correlation
What is geochemistry?
Looks at source rocks and oil typing
What is basin analysis?
Looks at structural, stratigraphic, reservoir, geochemical, resource estimation
Petroleum seismic surveying is more concerned with refracted or reflected ray paths?
Reflected
What are some applications of reflection seismic surveys?
Onshore : vibroseis energy source, geophones , recoring truck
Offshore: ship-based energy source (air guns), marine streamer (geophones), recorded onborad
What does a geophysical gravity survey measure??
What does it mean when there is an Excess and a Deficiency?
It measures rock density
Excess observed gravity produces a positive anomaly (high)
A deficiency produces a negative anomaly (low)
What does a geophysical magnetic survey measure?
It measures magnetic susceptability
What does a geophysical seismic survey measure?
It measures the time of acoustic wave transmission
Why does the gravitational acceleration on the Earth’s surface vary? 4 Factors
Latitude, Elevation, Topography, Geology
What is a correction(s) (in relation to the varying gravitational acceleration)
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
The Bouguer anomaly is what? explain what is required for it to happen and the resulting units
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
What is the application of a gravity map?
useful for showing the broad architecture of a sedimentary basin
When trying to locate salt domes and reefs VIA gravity maps what should you look for?
Salt = low gravity b/c extremely low density
Coral reef = high gravity b/c higher density
What’s the magnetic field strength at the poles vs the equator?
60,000 gamma (0.6 oersted) vs. 35,000 (0.35 oersted)
What is the purpose of a magnetic survey?
measure the field strength
Corrections done in magnetic survey remove what?
Changes in the Earth’s magnetic field
What three categories can open hole logs be placed into?
Natural Detection (SP, Gamma Ray)
Porosity (Sonic. Density, Neutron)
Resistivity (E-logs, Introduction, Laterologs)
What are the uses of well logs?
Determination of lithology
Evaluation of zones
Correlation of zones
What are the uses of well logs?
Determination of lithology
Evaluation of zones
Correlation of zones
What data can you measure from a core?
Porosity
Permeability
Oil and Water saturations (in 3 directions)
Grain density
Name 5 duties of the geologist
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)
What do mud loggers record?
rate of penetration
mud temperature
Pore pressure
Shale density
What monitors the presence of hydrocarbons in gas wells?
Gas chromatographs
Why is the rate of penetration a good indicator of the rock type and porosity?
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.
What 2 tests measure formation fluids and reservoir pressure?
Drillstem tests and repeat formation tests
Are DST’s open to surface?
YES
RFT’s are run on a wireline. Do they have open or closed sample chambers?
CLOSED
What 5 things are considerations of a good geologic prospect?
Good geologic factors Good economics Accessibility Subsurface rights Company risk profile
What 5 things should be included when compiling a geologic prospect?
Data collection Data manipulation Data interpretation The prospect map Selling the prospect
