Influence of oil wettability upon spectral induced polarization of oil-bearing sands

The presence of oil in an unconsolidated granular porous material, like a sand, changes both the resistivity of the material and the value of the phase lag between the current and the voltage. We performed laboratory experiments to investigate the influence of oil wettability and water saturation upon the complex resistivity of oil-bearing sands in the frequency range 1 mHz-1 kHz. For a sand saturated by a nonwetting oil, both the resistivity and the magnitude of the phase increase with the oil saturation, as expected from theoretical considerations. In the case of a sand partially saturated by a wetting oil, we found that both the magnitude of the phase and the resistivity decrease with the oil saturation. The quadrature conductivity decreases with the oil with the same trend in presence of wetting and nonwetting oils for relative water saturation above 0.5. In the case of a nonwetting oil, the results are quantitatively predicted by available theories. In the case of a wet oil, our results could be interpreted as resulting from the increase of the cation exchange capacity associated with the presence of a polar component at the oil water interface.