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Oil and Gas Formation
Terms in this set (9)
How is oil and gas formed?
Tiny sea plants and animals die, buried on ocean floor and covered by sedimentary rock. Buried deeper over millions of years, heat and pressure turn them into oil and gas.
At what depth and temp do oil and gas form?
300m - 50 - Diagenesis - Kerogen
1500m - 150 - Crude oil/Natural gas - Catagenesis
Below 4.2km - Carbon residue - nothing useful
Natural gas and petroleum makeup
Natural gas -99% methane, minor ethane, propane and butane
Petroleum - Mixture of numerous hydrocarbon compounds
Marine enviroments - Gasoline and kerogen prevalent
What makes an ideal area for petroleum to form?
"Seal" at top - impermeable rock
Permeable reservoir beneath
Example - Kimmeridge Clay - Major source rock in North sea
Source Rock - What makes it so?
Sufficient organic matter when buried + heated at depth
Organic rich mudstone and coal deposited in sub aqueous conditions
Depositional environments - Swamps, lakes, shallow marine environments
Reservoir Rock - What makes it so?
Porous and Permeable
Porous - Void space which can be filled by fluids and gas
Permeable - Ability of rock to transmit fluids through pore space
100-1000m - Best permeability for sandstone
Porosity DOES not mean permeable
Seals - What makes it so? Best attributes?
Rocks that reduce the online migration of fluids in subsurface
Small pore size
Ductile (Resist fracturing)
Thick rock units - Wide lateral extents
Traps - What makes it so?
Large scale petroleum container - contains economic amounts
Gas is less dense than oil, oil than water, they will rise through porous rock
Traps must be concave down and sealed
Structural and stratigraphic trap
Requirements for oil and gas to occur
Mature source rock
Large volumes in trap
Migration pathway between source and reservoir
Appropriate timing for these all to come together
This set is often in folders with...
Lecture 4: Sedimentary Structures
Oil and Gas Formation
Marine depositional environments
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