Dec2 Petroleum System
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Petroleum system
•Source Rock Hydrocarbon Generation•Migration
•Accumulation•Seal (cap rock)
•Trap (structural, stratigraphic)
Source rock hydrocarbon generation
• Organic matter
• Adequate T (“oil window”: 160-80o C)
• Sufficient time to bring the source rock to maturity
• Pressure and the presence of bacteria and catalysts can help generation
kerogen is a mixture of organic material (rather than a specific chemical), which makes up a portion of the organic matter in sedimentary rocks
Migration
• Movement of newly generated hydrocarbons out of their source rock (primary migration or expulsion)
• The further movement of the hydrocarbons into reservoir rocks (secondary migration)
• Migration usually occur from a structurally lower area to a higher area due to buoyancy of the hydrocarbons with respect to surrounding rocks.
• Migration can be local or over 100s of km.
Accumulation
• The phase in which the hydricarbons migrate into the reservoir and is trapped into it
Reservoir
• A subsurface body of rock having sufficient porosity and permeability to store and transmit fluids
• Which are the best reservoir rocks and why?
Types of porosity in sedimentary rocks
• Tight gas is the term commonly used to refer to low permeability reservoirs that produce mainly dry natural gas
Seal (cap rock)
• An impermeable rock that acts as a barrier to further migration of hydrocarbon liquids (shale, mudstone, anhydrite, salt)
Trap
• Structural traps (folds and faults)
• Stratigraphic traps (due to changes in rock type or pinch outs, unconformities or other sedimentary features sucha s reefs and buildups)