Investigation of the effect of heterogeneity on the resistivity of reservoir rock

Abstract

This research investigated the effect of rock heterogeneity on rock resistivity and consequently on the rock’s electrical parameters. Cores with similar values of porosity but with different porosity types were categorized as macroporosity, microporosity and mixed macro- and microporosity. From the capillary pressure curves and resistivity vs. saturation curves of the core samples, the saturation exponent, n, cementation factor, m, and irreducible water saturation Sun of the rocks were determined. It was initially observed that the saturation exponents of microporosity samples were extremely high, much higher than expected for core samples of these types. However, the corresponding capillary pressure curves showed that no significant de-saturation had taken place. On repetition of the desaturation of the samples by centrifuge, it was observed that the saturation exponents of macroporosity samples were higher than those of microporosity samples. A comparison of the saturation exponent, n against permeability, k showed the presence of three distinct clusters representing the three porosity types with the highest saturation exponents for macroporosity samples. In the comparison of cementation factor m vs. porosity, it was observed that for a particular set of samples, cementation factor, m increases with increasing porosity.