Changes

  | 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

  | frompg  = 5-60

  | topg    = 5-64

  | topg    = 5-60

  | 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

===Potential of water vs. hydrocarbons===

===Potential of water vs. hydrocarbons===

Fluid pressure equals pgH. Under hydrostatic conditions, the buoyant force equals

Fluid pressure equals ρgH. Under hydrostatic conditions, the buoyant force equals

:<math>\rho_{\rm w} \mbox{gH}_{\rm w} - \rho_{\rm h}\mbox{gH}_{\rm h}</math>

:<math>\rho_{\rm w} \mbox{gH}_{\rm w} - \rho_{\rm h}\mbox{gH}_{\rm h}</math>

* ρ_w = water density

* ρ_w = water density

* ρ_h = hydrocarbon density

* ρ_h = [[hydrocarbon]] density

* H_w = water depth

* H_w = water depth

* H_h = hydrocarbon column height

* H_h = [[hydrocarbon column]] height

Under hydrodynamic conditions, the potential for a hydrocarbon column (Φ_h) is related to the potential of the water by the equation

Under hydrodynamic conditions, the potential for a hydrocarbon column (Φ_h) is related to the potential of the water by the equation

:<math>\Phi_{\rm h} = \rho_{\rm h}\mbox{gH}_{\rm h} = \rho_{\rm w}\mbox{gH}_{\rm w} - (\rho_{\rm w} - \rho_{\rm h})\mbox{gZ}</math>

:<math>\Phi_{\rm h} = \rho_{\rm h}\mbox{gH}_{\rm h} = \rho_{\rm w}\mbox{gH}_{\rm w} - (\rho_{\rm w} - \rho_{\rm h})\mbox{gZ}</math>

Dividing through by g (ρ_w – ρ_h)/ρ_h to simplify gives (in a uniformly flat gravity field)

Dividing through by g (ρ_w – ρ_h)/ρ_h to simplify gives (in a uniformly flat [[gravity]] field)

:<math>\left(\frac{\rho_{\rm h}}{\rho_{\rm w} - \rho_{\rm h}}\right) \mbox{H}_{\rm h} = \left(\frac{\rho_{\rm w}}{\rho_{\rm w} - \rho_{\rm h}}\right)\mbox{H}_{\rm w} - \mbox{Z}</math>

:<math>\left(\frac{\rho_{\rm h}}{\rho_{\rm w} - \rho_{\rm h}}\right) \mbox{H}_{\rm h} = \left(\frac{\rho_{\rm w}}{\rho_{\rm w} - \rho_{\rm h}}\right)\mbox{H}_{\rm w} - \mbox{Z}</math>

Constant values for the left-hand side of the equation are equipotential surfaces for hydrocarbons. Hubbert<ref name=ch05r11>Hubbert, K., 1953, Entrapment of petroleum under hydrodynamic conditions: AAPG Bulletin, vol. 37, no. 8, p. 1954–2026. The original paper that proposed hydrodynamics as an important trapping mechanism.</ref> called this factor U. From the right side, constant values for ρ_w/(ρ_w – ρ_h)H_w are equipotential surfaces for water. Hubbert called this factor V. The elevation factor (Z) is the difference between the equipotential surfaces for hydrocarbons and water.

Constant values for the left-hand side of the equation are [[Wikipedia:Equipotential|equipotential]] surfaces for hydrocarbons. Hubbert<ref name=ch05r11>Hubbert, K., 1953, [http://archives.datapages.com/data/bulletns/1953-56/data/pg/0037/0008/1950/1954.htm Entrapment of petroleum under hydrodynamic conditions]: AAPG Bulletin, vol. 37, no. 8, p. 1954–2026. The original paper that proposed hydrodynamics as an important trapping mechanism.</ref> called this factor U. From the right side, constant values for ρ_w/(ρ_w – ρ_h)H_w are equipotential surfaces for water. Hubbert called this factor V. The elevation factor (Z) is the difference between the equipotential surfaces for hydrocarbons and water.

Substituting U and V in the above equation gives

Substituting U and V in the above equation gives

===Hydrodynamic effect on traps===

===Hydrodynamic effect on traps===

[[file:formation-fluid-pressure-and-its-application_fig5-37.png|thumb|{{figure number|1}}Modified. Copyright: North, 1985; courtesy Allen and Unwin.]]

[[file:formation-fluid-pressure-and-its-application_fig5-37.png|300px|thumb|{{figure number|1}}Vectors and equipotential lines for a hydrocarbon accumulation in an anticline in a hydrodynamic environment. Modified. Copyright: North;<ref name=North1985>North, F. K., 1985, Petroleum Geology: London, Allen & Unwin, 246 p.</ref> courtesy Allen and Unwin.]]

In a hydrostatic environment, the free-water level of a trap is horizontal. In a hydrodynamic environment, the free-water level of a trap is tilted because the buoyant force (P_b) is interfered with by the hydrodynamic force (P_w). The resultant interference is the vector known as the confining force (P_cf). U, an equipotential line, is perpendicular to P_cf and is tilted because of the effect of P_w. The diagram in [[:file:formation-fluid-pressure-and-its-application_fig5-37.png|Figure 1]] shows these vectors and the equipotential lines for a hydrocarbon accumulation in an anticline in a hydrodynamic environment.

In a hydrostatic environment, the free-water level of a trap is horizontal. In a hydrodynamic environment, the free-water level of a trap is tilted because the buoyant force (P_b) is interfered with by the hydrodynamic force (P_w). The resultant interference is the vector known as the confining force (P_cf). U, an equipotential line, is perpendicular to P_cf and is tilted because of the effect of P_w. The diagram in [[:file:formation-fluid-pressure-and-its-application_fig5-37.png|Figure 1]] shows these vectors and the equipotential lines for a hydrocarbon [[accumulation]] in an [[anticline]] in a hydrodynamic environment.

==See also==

==See also==

[[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]]