Oil and Gas Formation
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
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 Accessible Regional seal Migration pathway between source and reservoir Appropriate timing for these all to come together
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
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 Best attributes Small pore size Ductile (Resist fracturing) Thick rock units - Wide lateral extents
What makes an ideal area for petroleum to form?
Source rock "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
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. Planktonic microorganisms
