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Hydrocarbon expulsion, migration, and accumulation (view source)
Revision as of 17:09, 31 January 2014
, 17:09, 31 January 2014Initial import
{{publication
| image = exploring-for-oil-and-gas-traps.png
| width = 120px
| series = Treatise in Petroleum Geology
| title = Exploring for Oil and Gas Traps
| part = Predicting the occurrence of oil and gas traps
| chapter = Predicting reservoir system quality and performance
| frompg = 9-1
| topg = 9-156
| author = Dan J. Hartmann, Edward A. Beaumont
| link = http://archives.datapages.com/data/specpubs/beaumont/ch09/ch09.htm
| pdf =
| store = http://store.aapg.org/detail.aspx?id=545
| isbn = 0-89181-602-X
}}
The pores and fluids of a reservoir system interact during the processes of expulsion, [[migration]], accumulation, and flow to a wellbore. Differential pressure (ΔP) in the fluid continuum of the [[petroleum system]], caused by properties of fluids and pores, controls these processes.
==Expulsion==
Hydrocarbon generation causes pressure build-up in the [[source rock]], exceeding the pore pressure of the adjacent aquifer. Oil or gas is expelled or “squeezed” into the aquifer due to the differential pressures between source rock and aquifer fluid.
==Migration==
Hydrocarbon migrates through an aquifer when it is “buoyed” upward due to AP caused by the density differential of the hydrocarbons and the formation water. The oil or gas migrates in filaments through the pore system of the aquifer as long as the [[buoyancy pressure]] (P<sub>b</sub>) exceeds the capillary resistance of the water in the pore throats. This relationship is illustrated in the diagram below.
For migration to continue as pore throat size decreases from one site to the next (points A and B in Figure 9-14), the length of the filament (''h'') must increase until an adequate P<sub>b</sub> exists across the pore throat to initiate breakthrough.
[[file:predicting-reservoir-system-quality-and-performance_fig9-14.png|thumb|{{figure number|9-14}}After .<ref name=ch09r6>Berg, R., 1975, [[Capillary pressure]]s in [[stratigraphic trap]]s: AAPG Bulletin, vol. 59, no. 6, p. 939–956.</ref>]]
==Accumulation==
A hydrocarbon accumulation forms when migrating hydrocarbon filaments encounter a zone (the seal), either laterally or vertically, with pore throat sizes smaller than the carrier bed. The seal pore throat breakthrough pressure or the distance to the spill point of the trap, whichever is less, determines the hydrocarbon accumulation column height.
==[[Buoyancy pressure]] profile==
When a reservoir has formed in a trap and has come to pressure equilibrium with the water in the aquifer, the pore pressure of the hydrocarbons at different depths in the reservoir plot along a steeper gradient than the water gradient. The figure below shows this relationship.
[[file:predicting-reservoir-system-quality-and-performance_fig9-15.png|thumb|{{figure number|9-15}}. Copyright: Coalson et al., 1994; courtesy RMAG.]]
The pressure contrast between the hydrocarbon gradient and the water gradient at a given depth in the reservoir (height above free water) is the buoyancy pressure (P<sub>b</sub>). The longer the column, the higher the P<sub>b</sub> at the top of the column.
==Water saturation==
The water remaining on the surfaces of the pores and pore throats of a rock after hydrocarbon has driven (drained) out the rest of the water is called the '''residual water saturation''' (S<sub>wr</sub>). P<sub>b</sub> provides the energy needed to overcome the capillary resistance of the water in the pore throat and drive down S<sub>wr</sub> in the pore. The higher a portion of the reservoir (with a given [[capillary pressure]] profile-pore type) occurs above the zero [[pressure::(0 psi]]) P<sub>b</sub> position, the lower its S<sub>wr</sub> will become. Consequently, an S<sub>wr</sub> model can be developed from capillary pressure profiles because S<sub>wr</sub> is a function of the profile of pore throat sizes and height above P<sub>b</sub> = [[pressure::0 psi]].
==See also==
* [[Pore–fluid interaction]]
* [[Characterizing rock quality]]
* [[Pc curves and saturation profiles]]
* [[Converting Pc curves to buoyancy, height, and pore throat radius]]
* [[What is permeability?]]
* [[Relative permeability and pore type]]
==References==
{{reflist}}
==External links==
{{search}}
* [http://archives.datapages.com/data/specpubs/beaumont/ch09/ch09.htm Original content in Datapages]
* [http://store.aapg.org/detail.aspx?id=545 Find the book in the AAPG Store]
[[Category:Predicting the occurrence of oil and gas traps]]
[[Category:Predicting reservoir system quality and performance]]
| image = exploring-for-oil-and-gas-traps.png
| width = 120px
| series = Treatise in Petroleum Geology
| title = Exploring for Oil and Gas Traps
| part = Predicting the occurrence of oil and gas traps
| chapter = Predicting reservoir system quality and performance
| frompg = 9-1
| topg = 9-156
| author = Dan J. Hartmann, Edward A. Beaumont
| link = http://archives.datapages.com/data/specpubs/beaumont/ch09/ch09.htm
| pdf =
| store = http://store.aapg.org/detail.aspx?id=545
| isbn = 0-89181-602-X
}}
The pores and fluids of a reservoir system interact during the processes of expulsion, [[migration]], accumulation, and flow to a wellbore. Differential pressure (ΔP) in the fluid continuum of the [[petroleum system]], caused by properties of fluids and pores, controls these processes.
==Expulsion==
Hydrocarbon generation causes pressure build-up in the [[source rock]], exceeding the pore pressure of the adjacent aquifer. Oil or gas is expelled or “squeezed” into the aquifer due to the differential pressures between source rock and aquifer fluid.
==Migration==
Hydrocarbon migrates through an aquifer when it is “buoyed” upward due to AP caused by the density differential of the hydrocarbons and the formation water. The oil or gas migrates in filaments through the pore system of the aquifer as long as the [[buoyancy pressure]] (P<sub>b</sub>) exceeds the capillary resistance of the water in the pore throats. This relationship is illustrated in the diagram below.
For migration to continue as pore throat size decreases from one site to the next (points A and B in Figure 9-14), the length of the filament (''h'') must increase until an adequate P<sub>b</sub> exists across the pore throat to initiate breakthrough.
[[file:predicting-reservoir-system-quality-and-performance_fig9-14.png|thumb|{{figure number|9-14}}After .<ref name=ch09r6>Berg, R., 1975, [[Capillary pressure]]s in [[stratigraphic trap]]s: AAPG Bulletin, vol. 59, no. 6, p. 939–956.</ref>]]
==Accumulation==
A hydrocarbon accumulation forms when migrating hydrocarbon filaments encounter a zone (the seal), either laterally or vertically, with pore throat sizes smaller than the carrier bed. The seal pore throat breakthrough pressure or the distance to the spill point of the trap, whichever is less, determines the hydrocarbon accumulation column height.
==[[Buoyancy pressure]] profile==
When a reservoir has formed in a trap and has come to pressure equilibrium with the water in the aquifer, the pore pressure of the hydrocarbons at different depths in the reservoir plot along a steeper gradient than the water gradient. The figure below shows this relationship.
[[file:predicting-reservoir-system-quality-and-performance_fig9-15.png|thumb|{{figure number|9-15}}. Copyright: Coalson et al., 1994; courtesy RMAG.]]
The pressure contrast between the hydrocarbon gradient and the water gradient at a given depth in the reservoir (height above free water) is the buoyancy pressure (P<sub>b</sub>). The longer the column, the higher the P<sub>b</sub> at the top of the column.
==Water saturation==
The water remaining on the surfaces of the pores and pore throats of a rock after hydrocarbon has driven (drained) out the rest of the water is called the '''residual water saturation''' (S<sub>wr</sub>). P<sub>b</sub> provides the energy needed to overcome the capillary resistance of the water in the pore throat and drive down S<sub>wr</sub> in the pore. The higher a portion of the reservoir (with a given [[capillary pressure]] profile-pore type) occurs above the zero [[pressure::(0 psi]]) P<sub>b</sub> position, the lower its S<sub>wr</sub> will become. Consequently, an S<sub>wr</sub> model can be developed from capillary pressure profiles because S<sub>wr</sub> is a function of the profile of pore throat sizes and height above P<sub>b</sub> = [[pressure::0 psi]].
==See also==
* [[Pore–fluid interaction]]
* [[Characterizing rock quality]]
* [[Pc curves and saturation profiles]]
* [[Converting Pc curves to buoyancy, height, and pore throat radius]]
* [[What is permeability?]]
* [[Relative permeability and pore type]]
==References==
{{reflist}}
==External links==
{{search}}
* [http://archives.datapages.com/data/specpubs/beaumont/ch09/ch09.htm Original content in Datapages]
* [http://store.aapg.org/detail.aspx?id=545 Find the book in the AAPG Store]
[[Category:Predicting the occurrence of oil and gas traps]]
[[Category:Predicting reservoir system quality and performance]]