Carbonate Reservoir Rocks Show Induced Polarization Effects, Based on Generalized Effective Medium Theory

Abstract

The analysis of electrical induced polarization (IP) effects has a growing interest in oil and gas exploration. Recent electromagnetic surveys in Saudi Arabia revealed resistivity dispersive variations in agreement with fluid distribution in the surveyed reservoirs. This paper demonstrates that two selected carbonate reservoir formations, typical of Saudi Arabia, show in the laboratory distinct IP responses that are statistically repeatable. Reservoir rocks saturated with crude oil are observed to have different and distinct complex resistivity (CR) spectra than the same reservoir rocks saturated with brine. Therefore, IP methods have the potential to provide a basis for in situ fluid discrimination. We demonstrate also that using the analysis based on Generalized Effective Medium Theory of Induced Polarization (GEMTIP) one can invert the observed CR spectra for meaningful rock and fluid properties, such as fluid saturations and porosity. GEMTIP based inversion also recovers the resistivities of the fluids in the rock samples, thereby becoming feasible to produce 3D models of porosity and fluid (oil and water) saturations from the 3D models of resistivity and chargeability, as recovered from the GEMTIP based 3D inversion of the large scale field IP data.