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)