40 PETROLEUM TECHNOLOGY, ECONOMICS, AND POLITICS
Table 2.2 General mechanisms for petroleum migration.
Geological Event
Basin development
Mature basin
Hydrocarbon generation
Hydrocarbons dissolve
Geothermal gradient changes
Pore fluids cool
Hydrocarbons separate
Updip migration
Intermittent faulting
Migration Effect
downward fluid flow
sediments move downward
thermal effects on source
sediment
pore fluid become saturated
isotherms depressed
hydrocarbons form separate
phase
move to top of carrier fluid
(water)
buoyancy effect
hydrocarbon migration to traps
The distribution of the fluids in a reservoir rock is dependent on
the densities of the fluids as well as on the properties of the rock. If
the pores are of uniform size and evenly distributed, there is:
1. an upper zone where the pores are filled mainly by gas
(the gas cap).
2. a middle zone in which the pores are occupied principally by oil with gas in solution.
3. a lower zone with its pores filled by water.
Approximately 10 to 30% of water occurs along with the oil in
the middle zone. There is a transition zone from the pores occupied entirely by water to pores occupied mainly by oil in the reservoir rock, and the thickness of this zone depends on the densities
and interfacial tension of the oil and water, as well as the sizes of
the pores. Similarly, there is some water in the pores in the upper
gas zone that has at its base a transition zone from pores occupied
largely by gas to pores filled mainly by oil.
The water found in the oil and gas zones is known generally as
interstitial water. It usually occurs as collars around grain contacts,
Table 2.2 General mechanisms for petroleum migration.
Geological Event
Basin development
Mature basin
Hydrocarbon generation
Hydrocarbons dissolve
Geothermal gradient changes
Pore fluids cool
Hydrocarbons separate
Updip migration
Intermittent faulting
Migration Effect
downward fluid flow
sediments move downward
thermal effects on source
sediment
pore fluid become saturated
isotherms depressed
hydrocarbons form separate
phase
move to top of carrier fluid
(water)
buoyancy effect
hydrocarbon migration to traps
The distribution of the fluids in a reservoir rock is dependent on
the densities of the fluids as well as on the properties of the rock. If
the pores are of uniform size and evenly distributed, there is:
1. an upper zone where the pores are filled mainly by gas
(the gas cap).
2. a middle zone in which the pores are occupied principally by oil with gas in solution.
3. a lower zone with its pores filled by water.
Approximately 10 to 30% of water occurs along with the oil in
the middle zone. There is a transition zone from the pores occupied entirely by water to pores occupied mainly by oil in the reservoir rock, and the thickness of this zone depends on the densities
and interfacial tension of the oil and water, as well as the sizes of
the pores. Similarly, there is some water in the pores in the upper
gas zone that has at its base a transition zone from pores occupied
largely by gas to pores filled mainly by oil.
The water found in the oil and gas zones is known generally as
interstitial water. It usually occurs as collars around grain contacts,