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{{Merge|Pressure compartments}}
 
{{publication  
 
{{publication  
 
  | image  = exploring-for-oil-and-gas-traps.png
 
  | image  = exploring-for-oil-and-gas-traps.png
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  | part    = Critical elements of the petroleum system
 
  | part    = Critical elements of the petroleum system
 
  | chapter = Formation fluid pressure and its application
 
  | chapter = Formation fluid pressure and its application
  | frompg  = 5-1
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  | frompg  = 5-45
  | topg    = 5-64
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  | topg    = 5-47
 
  | author  = Edward A. Beaumont, Forrest Fiedler
 
  | author  = Edward A. Beaumont, Forrest Fiedler
 
  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch05/ch05.htm
 
  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch05/ch05.htm
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}}
 
}}
 
==Definition==
 
==Definition==
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[[file:formation-fluid-pressure-and-its-application_fig5-22.png|300px|thumb|{{figure number|1}}Schematic cross section and pressure-depth plot showing how changes in the fluid pressure gradient correlate with the top and bottom seals of a regional pressure compartment in a foreland basin.]]
    
Most deep sedimentary basins of the world contain a shallow, normally pressured hydraulic system overlying one or more hydraulic compartments whose pressures are above or below the normal static water pressure.<ref name=ch05r14>Powley, D., E., 1990, Pressures and hydrogeology in petroleum basins: Earth Science Reviews, vol. 29, p. 215–226.</ref> In this discussion these hydraulic compartments are called '''pressure compartments'''. They are defined within a basin from pressure measurements.
 
Most deep sedimentary basins of the world contain a shallow, normally pressured hydraulic system overlying one or more hydraulic compartments whose pressures are above or below the normal static water pressure.<ref name=ch05r14>Powley, D., E., 1990, Pressures and hydrogeology in petroleum basins: Earth Science Reviews, vol. 29, p. 215–226.</ref> In this discussion these hydraulic compartments are called '''pressure compartments'''. They are defined within a basin from pressure measurements.
    
==Seals==
 
==Seals==
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[[file:formation-fluid-pressure-and-its-application_fig5-23.png|300px|thumb|{{figure number|2}}Cross section illustrating the multiple pressure compartments of the Anadarko basin. From Bradley and Powley;<ref name=BandP1995>Bradley, J. S., and D. E. Powley, 1995, [http://archives.datapages.com/data/specpubs/memoir61/ch01/0001.htm  Pressure compartments in sedimentary basins], in P.J. Ortoleva, ed., Basin Compartments and Seals: [http://store.aapg.org/detail.aspx?id=748 AAPG Memoir 61], p. 3–26.</ref> courtesy AAPG.]]
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Seals isolate fluids within compartments from fluids that are in pressure communication with the surface (normally pressured hydraulic system). The '''top seal''' is more or less horizontal and usually cuts across stratigraphic units. It forms where authigenic minerals (usually calcite) fill the pore spaces. The '''bottom seal''' of regional compartments is usually a well defined lithostratigraphic unit. Commonly, the '''side seals''' are thin, mineralized zones paralleling vertical faults.
 
Seals isolate fluids within compartments from fluids that are in pressure communication with the surface (normally pressured hydraulic system). The '''top seal''' is more or less horizontal and usually cuts across stratigraphic units. It forms where authigenic minerals (usually calcite) fill the pore spaces. The '''bottom seal''' of regional compartments is usually a well defined lithostratigraphic unit. Commonly, the '''side seals''' are thin, mineralized zones paralleling vertical faults.
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==Schematic of pressure compartment==
 
==Schematic of pressure compartment==
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[[file:formation-fluid-pressure-and-its-application_fig5-22.png|thumb|{{figure number|1}}See text for explanation.]]
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The schematic [[cross section]] and pressure-depth plot in [[:file:formation-fluid-pressure-and-its-application_fig5-22.png|Figure 1]] shows how changes in the fluid pressure gradient correlate with the top and bottom seals of a regional pressure compartment in a [[foreland basin]].
 
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The schematic cross section and pressure-depth plot in [[:file:formation-fluid-pressure-and-its-application_fig5-22.png|Figure 1]] shows how changes in the fluid pressure gradient correlate with the top and bottom seals of a regional pressure compartment in a foreland basin.
      
==Multiple pressure compartments==
 
==Multiple pressure compartments==
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[[file:formation-fluid-pressure-and-its-application_fig5-23.png|left|thumb|{{figure number|2}}.]]
      
Many sedimentary basins contain two or more pressure compartments. The cross section in [[:file:formation-fluid-pressure-and-its-application_fig5-23.png|Figure 2]] illustrates the multiple pressure compartments of the Anadarko basin.
 
Many sedimentary basins contain two or more pressure compartments. The cross section in [[:file:formation-fluid-pressure-and-its-application_fig5-23.png|Figure 2]] illustrates the multiple pressure compartments of the Anadarko basin.
    
==Regional pressure compartment==
 
==Regional pressure compartment==
The cross section below illustrates a regional pressure compartment from the Anadarko basin of Oklahoma.
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[[file:formation-fluid-pressure-and-its-application_fig5-24.png|thumb|{{figure number|5-24}}.]]
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[[file:formation-fluid-pressure-and-its-application_fig5-24.png|300px|thumb|{{figure number|3}}Cross section illustrating a regional pressure compartment from the Anadarko basin of Oklahoma. From Al-Shaieb et al.;<ref name=AlShaieb1995a /> courtesy AAPG.]]
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The cross section in [[:file:formation-fluid-pressure-and-its-application_fig5-24.png|Figure 3]] illustrates a regional pressure compartment from the Anadarko basin of Oklahoma.
    
==Example: gradient profile==
 
==Example: gradient profile==
Following is a pressure-depth plot of a well through the Anadarko regional pressure cornpartment. Fluid pressure goes from normal above the top seal to overpressured within the pressure compartment, then back to normal below the bottom seal. Many regional pressure compartments contain smaller subregional and local pressure compartments. Al-Shaieb et al.<ref name=ch05r2>Al-Shaieb, Z., Puckette, J., O., Abdalla, A., A., Ely, P., B., 1995b, Three levels of compartmentation within the overpressured interval of the Anadarko basin, in Ortoleva, P., J., ed., Basin Compartments and Seals: AAPG Memoir 61, p. 69–83.</ref> use the following terms:
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[[file:formation-fluid-pressure-and-its-application_fig5-25.png|300px|thumb|{{figure number|4}}Fluid pressure gradient variations within the pressure compartment on the plot represent the smaller second- and third-order compartments. Modified from Al-Shaieb et al.;<ref name=AlShaieb1995a>Al-Shaieb, Z., J. O. Puckette, A. A. Abdalla, and P. B. Ely, 1995a, [http://archives.datapages.com/data/specpubs/memoir61/ch04/0055.htm Megacompartment complex in the Anadarko basin], in P. J. Ortoleva, ed., Basin Compartments and Seals: [http://store.aapg.org/detail.aspx?id=748 AAPG Memoir 61], p. 55–68.</ref> courtesy AAPG.]]
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Following is a pressure-depth plot of a well through the Anadarko regional pressure cornpartment. Fluid pressure goes from normal above the top seal to overpressured within the pressure compartment, then back to normal below the bottom seal. Many regional pressure compartments contain smaller subregional and local pressure compartments. Al-Shaieb et al.<ref name=ch05r2>Al-Shaieb, Z., Puckette, J., O., Abdalla, A., A., Ely, P., B., 1995b, [http://archives.datapages.com/data/specpubs/memoir61/ch05/0069.htm Three levels of compartmentation within the overpressured interval of the Anadarko basin], in Ortoleva, P., J., ed., Basin Compartments and Seals: [http://store.aapg.org/detail.aspx?id=748 AAPG Memoir 61], p. 69–83.</ref> use the following terms:
    
* Regional pressure compartments—first-order or mega-compartments
 
* Regional pressure compartments—first-order or mega-compartments
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* Local compartments—third-order compartments
 
* Local compartments—third-order compartments
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The fluid pressure gradient variations within the pressure compartment on the plot below represent the smaller second- and third-order compartments.
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The fluid pressure gradient variations within the pressure compartment on the plot in [[:file:formation-fluid-pressure-and-its-application_fig5-25.png|Figure 4]] represent the smaller second- and third-order compartments.
 
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[[file:formation-fluid-pressure-and-its-application_fig5-25.png|thumb|{{figure number|5-25}}Modified.]]
      
==See also==
 
==See also==
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[[Category:Critical elements of the petroleum system]]  
 
[[Category:Critical elements of the petroleum system]]  
 
[[Category:Formation fluid pressure and its application]]
 
[[Category:Formation fluid pressure and its application]]
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[[Category:Treatise Handbook 3]]

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