@wikipedia
Synonym: Pore Compressibility = CPHI
A measure of formation porosity
change due to reservoir pressure variation:| LaTeX Math Block |
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c_r\phi = \frac{1}{\phi} \frac{\partial \phi}{\partial p} |
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There is a statistical correlation between initial formation compressibility
and
formation porosity which can be picked by various
compressibility-porosity models.
Pore compressibility stays constant for small pressure variations but in a wide range of pressure variations the dependence on ambient pressure
can not be neglected and should be tabulated from laboratory core tests or estimated from
compressibility-pressure correlations.
The typical values are in :
cϕ = 0.5 ÷ 1.5 GPa-1
but may go higher for poorly consolidated rocks.
In many practical cases the pore compressibility can be considered as poorly dependent on reservoir pressure variation:
| LaTeX Math Inline |
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| body | 0.5 \div 1.5 \cdot 10^{-6} \, {\rm kPa}^{-1} |
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but may go higher for poorly consolidated rocks.See also
...
| c_\phi(p) = c_\phi = \rm const |
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.In this case porosity dependence on reservoir pressure can be simulated as:
| LaTeX Math Block |
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\phi(p) = \phi_i \cdot \left[ 1 + c_\phi \, (p-p_i) + 0.5 \, c^2_\phi \, (p-p_i)^2 \right] |
But in case the reservoir pressure is changing substantially one may need to account for the effect it takes on pore compressibility (see Pore compressibility @model) and then reservoir pressure - porosity model is going to take the following form:
| LaTeX Math Block |
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\phi(p) = \phi_i \cdot \exp \left[ \int_{p_i}^p c_\phi\, dp \right] |
See Also
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Petroleum Industry / Upstream / Subsurface E&P Disciplines / Petrophysics / Geomechanical Rock Modelling
[Compressibility][ initial pore compressibility ]
[ Compressibility (rock) ]
[ Pore compressibility @model ]
