In many practical cases the pore compressibility can be considered as independent on reservoir pressure variation:

But in case the reservoir pressure is changing substantially one may need to account for the effect it takes on pore compressibility.

The model usually relates Empirical crrelation between pore compressibility 

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\displaystyle c_r\phi(p) = c_{ri\phi i} \cdot \frac{ \ln \left( \frac{ p_n }{p_{\rm max}} \right)  }{ \ln \left( \frac{p_{ni}}{p_{\rm max}} \right)  }

p_n = p_{\rm min} + 1.75 \cdot \phi^{0.51} \cdot (p_{\rm max} - p) 

p_{ni} = p_{\rm min} + 1.75 \cdot \phi^{0.51} \cdot (p_{\rm max} - p_i) 

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But in case the reservoir pressure is changing substantially one may need to account for the effect it takes on pore compressibility which can be fairly approximated by Dobrynin correlation

See also

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Petroleum Industry / Upstream / Subsurface E&P Disciplines / Petrophysics / Geomechanical Rock Modelling / Pore compressibility