The porosity exponent (m) in the Archie saturation equation is very variable in carbonates. In this study – in a heterogeneous coquina carbonate a numerical study using a micro-CT volume in a resistivity model to calculate formation factor to compare with experimental data. The calibrated model is then used to explore the issues of the representative elementary volume, the heterogeneity and the anisotropy. The range of m from 1.6 to 3.8 is explained by varying tortuosity. This has implications understanding porosity exponent in carbonates and in resistivity-based formation evaluation in coquina carbonates.


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