Motivation
The most accurate way to simulate Gas Cap expansion (or shrinkage) is full-field 3D Dynamic Flow Model where Gas Cap 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. Unfortunately, in many practical cases the detailed information on the Gas Cap is not available. Besides many practical applications require only knowledge of one element of the Gas Cap expansion process – a pressure support and not the sweep in the invaded zones. This allows building a Gas Cap Drive @model using analytical methods.
Inputs & Outputs
Inputs | Outputs | ||
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p_i | Initial formation pressure | Q^{\downarrow}_{GC}(t) | Cumulative flux of gas from Gas Cap |
V_{GC, \, 0} | Initial Gas Cap volume | q^{\downarrow}_{GC}(t) = \frac{dQ^{\downarrow}_{GC}}{dt} | Volumetric gas flowrate from Gas Cap |
c_g(p) | Gas compressibility |
Assumptions
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] |
Equations
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Approximations
In case when pressure depletion \displaystyle \frac{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 Drive
[ Depletion ] [ Saturated oil reservoir ]