Hydrocarbon column: calculation of maximum height
Calculation
The maximum column of hydrocarbons that can accumulate under a seal occurs when the buoyancy pressure, Pb, equals the displacement pressure, Pd. If Pb exceeds Pd, the hydrocarbons will leak through the seal. If Pb is less than Pd, it would be possible to seal a greater column of hydrocarbons.
Therefore, for the maximum hydrocarbon column
or, in mixed units,
where:
- ρw = density of water, g/cm3
- ρh = density of hydrocarbon, g/cm3
- g = acceleration due to gravity, cm/sec2
- h = thickness of the hydrocarbon column, ft or m
- γ is the interfacial tension,
- θ is the contact angle between the wetting fluid and the solid surface, and
- R is the capillary (pore throat) radius (Vavra et al., 1992[citation needed]).
Effect on seal capacity
The height of the hydrocarbon column (h) in the above equations is a theoretical maximum. The actual height is less because of the effect of the reservoir. If the reservoir itself had zero displacement pressure, the height of the hydrocarbon column would attain the theoretical maximum and the oil-water contact would coincide with the free water level. If the reservoir has some displacement pressure greater than zero, then the height of the hydrocarbon column is less than the theoretical maximum, or
where:
- Pds = displacement pressure of the seal
- Pdr = displacement pressure of the reservoir
See also
External links
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