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Merged Buoyant pressure article into this one
Following the path of least capillary resistance, [[nonwetting fluids]] (gas or nonwetting oil) first move into the pore system that has the largest [[Pore and pore throat sizes|pore throats]]. Later, as the [[Hydrocarbon column|column height]] of the oil or gas grows and the buoyancy pressure increases, the hydrocarbons begin migrating into pores with smaller and smaller pore throats (in a [[water-wet system]]).
Following the path of least capillary resistance, [[nonwetting fluids]] (gas or nonwetting oil) first move into the pore system that has the largest [[Pore and pore throat sizes|pore throats]]. Later, as the [[Hydrocarbon column|column height]] of the oil or gas grows and the buoyancy pressure increases, the hydrocarbons begin migrating into pores with smaller and smaller pore throats (in a [[water-wet system]]).
==Calculation==
The buoyant pressure (P<sub>b</sub>) exerted by a [[Hydrocarbon column|column of hydrocarbons]] against the overlying seal is as follows:
:<math>\mbox{P}_{\rm b} = (\rho_{\rm w} - \rho_{\rm h}) \mbox{gh}</math>
Or, in the mixed units of the oil field:
:<math>\mbox{P}_{\rm b} = (\rho_{\rm w} - \rho_{\rm h}) 0.433 \mbox{ h}</math>
where:
* ρ<sub>w</sub> = density of water, g/cm<sup>3</sup>
* ρ<sub>h</sub> = density of hydrocarbon, g/cm<sup>3</sup>
* g = acceleration due to gravity, cm/sec<sup>2</sup>
* h = thickness of the hydrocarbon column, ft or m
==Pressure-depth plot==
[[file:evaluating-top-and-fault-seal_fig10-47.png|300px|thumb|{{figure number|1}}Pressure-depth plot through an oil column trapped beneath a top seal.]]
[[:file:evaluating-top-and-fault-seal_fig10-47.png|Figure 1]] is a pressure-depth plot through an oil column trapped beneath a top seal. The buoyant pressure of the oil column at any depth is the difference in pressure between the oil gradient and the water gradient. The maximum buoyant pressure (P<sub>max</sub>) is at the crest of the oil column. The buoyant pressure is zero at the [[free water level]] (FWL).
==See also==
==See also==
* [[Capillary pressure]]
* [[Capillary pressure]]
* [[How capillary properties control seal]]
* [[Top seal displacement pressure]]
* [[Hydrocarbon column: calculation of maximum height]]
==External links==
==External links==