The most accurate way to simulate gas expansion is conventional 3D full-field dynamic modelling where gas expansion is treated as one of the fluid phases and accounts of geological heterogeneities, gas fluid properties, relperm properties and heat exchange with surrounding rocks.
The analytical models usually assume:
Isothermal expansion | Uniform pressure depletion in Gas Cap |
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T = \rm const | p_{GC}(t) = p(t) |
which leads to the following equation for Gas Cap volume:
(1) | V_{GC}(t) = V_{GC}(0) \cdot \exp \left[ - \int_{p_i}^{p(t)} c_g(p) dp \right] |
and correspondingly to following Gas Cap Drive model:
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In case when pressure depletion ( p(t)/p_i) is not severe then compressibility factor maybe considered as relatively constant Z = \rm const which leads to \displaystyle c_g = \frac{1}{p} and:
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See Also
Petroleum Industry / Upstream / Subsurface E&P Disciplines / Field Study & Modelling / Gas Cap Expansion
[ Depletion ] [ Saturated oil reservoir ]