Changes

  | part    = Predicting the occurrence of oil and gas traps

  | part    = Predicting the occurrence of oil and gas traps

  | chapter = Predicting reservoir system quality and performance

  | chapter = Predicting reservoir system quality and performance

  | frompg  = 9-1

  | frompg  = 9-27

  | topg    = 9-156

  | topg    = 9-28

  | author  = Dan J. Hartmann, Edward A. Beaumont

  | author  = Dan J. Hartmann, Edward A. Beaumont

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch09/ch09.htm

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch09/ch09.htm

  | isbn    = 0-89181-602-X

  | 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.

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==

==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.

Expulsion describes the movement of hydrocarbons from the petroleum source rock into the carrier bed or migration conduit.  The expulsion event is driven by a combination of factors that include compaction, chemical reactions, source richness, [[kerogen]] type, and thermal expansion.  [[Petroleum generation|Hydrocarbon generation]] causes pressure build-up in the [[source rock]], exceeding the pore pressure of the adjacent carrier bed. Oil or gas is expelled or “squeezed” into the carrier bed due to the differential pressures between source rock and fluid in the carrier bed.

==Migration==

==Migration==

[[file:predicting-reservoir-system-quality-and-performance_fig9-14.png|thumb|{{figure number|1}}After .<ref name=ch09r6>Berg, R., 1975, [http://archives.datapages.com/data/bulletns/1974-76/data/pg/0059/0006/0900/0939.htm Capillary pressures in stratigraphic traps]: AAPG Bulletin, vol. 59, no. 6, p. 939–956.</ref>]]

[[file:predicting-reservoir-system-quality-and-performance_fig9-14.png|300px|thumb|{{figure number|1}}Relationship between the buoyancy pressure (P_b) and the capillary resistance of the water. After Berg.<ref name=ch09r6>Berg, R., 1975, [http://archives.datapages.com/data/bulletns/1974-76/data/pg/0059/0006/0900/0939.htm Capillary pressures in stratigraphic traps]: AAPG Bulletin, vol. 59, no. 6, p. 939–956.</ref>]]

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_b) exceeds the capillary resistance of the water in the pore throats. This relationship is illustrated in the diagram below.

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_b) exceeds the capillary resistance of the water in the pore throats. This relationship is illustrated in [[:file:predicting-reservoir-system-quality-and-performance_fig9-14.png|Figure 1]].

For migration to continue as pore throat size decreases from one site to the next (points A and B in [[:file:predicting-reservoir-system-quality-and-performance_fig9-14.png|Figure 1]]), the length of the filament (''h'') must increase until an adequate P_b exists across the pore throat to initiate breakthrough.

For migration to continue as pore throat size decreases from one site to the next (points A and B in [[:file:predicting-reservoir-system-quality-and-performance_fig9-14.png|Figure 1]]), the length of the filament (''h'') must increase until an adequate P_b exists across the pore throat to initiate breakthrough.

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.

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==

==Buoyancy pressure profile==

[[file:predicting-reservoir-system-quality-and-performance_fig9-15.png|thumb|{{figure number|9-15}}. Copyright: Coalson et al., 1994; courtesy RMAG.]]

[[file:predicting-reservoir-system-quality-and-performance_fig9-15.png|300px|thumb|{{figure number|2}}Relationship between the hydrocarbon gradient and water gradient. From Coalson et al.<ref name=Coalsonetal_1994>Coalson, E. B., S. M. Goolsby, and M. H. Franklin, 1994, Subtle seals and fluid-flow barriers in carbonate rocks, ''in'' J. C. Dolson, M. L. Hendricks, and W. A. Wescott, eds., Unconformity related hydrocarbons in sedimentary sequences: Rocky Mountain Association of Geologists (RMAG) Guidebook for Petroleum Exploration and Exploitation in Clastic and Carbonate Sediments, p. 45-58.</ref> 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_b). The longer the column, the higher the P_b at the top of the column.

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_b). The longer the column, the higher the P_b at the top of the column.

==See also==

==See also==

* [[Pore–fluid interaction]]

* [[Pore-fluid interaction]]

* [[Characterizing rock quality]]

* [[Characterizing rock quality]]

* [[Pc curves and saturation profiles]]

* [[Pc curves and saturation profiles]]

[[Category:Predicting the occurrence of oil and gas traps]]  

[[Category:Predicting the occurrence of oil and gas traps]]  

[[Category:Predicting reservoir system quality and performance]]

[[Category:Predicting reservoir system quality and performance]]