A Comprehensive Study of the Relative Dielectric Permittivity in Porous Media

Abstract

AbstractThis study investigated the effects of water saturation and wettability on the dielectric permittivity experimentally, using four-electrode impedance measurements, and theoretically, using models that account for the electrical double layer polarization.Complex impedance measurements, performed on Berea sandstone and on Ottawa-sand packs in the frequency range 10 Hz to 1 MHz, indicated a linearly varying relative dielectric permittivity with water saturations above 50%. The rate of change of the relative dielectric permittivity with saturation decreased as the frequency increased.The relative dielectric permittivity of water-wet samples was higher than that of the oil-wet samples at all water saturations. The difference was more pronounced as the saturation increased. The relative change was approximately 60% at a water saturation of 100%. To confirm these experimental observations, this study conducted simulations of rock wettability changes using a generalized Maxwell-Wagner model by varying the amount of ionic surface charge of rocks. In general oil-wetting agents react with the formation matrix by connecting their positively charged tails to the negatively charged silica surfaces, lowering the surface charge density. Simulations showed that there was about an order of magnitude difference in the relative dielectric permittivity as the rock surface charge changed by an order of magnitude. Both simulations and experimental results showed a trend of significant increase in the relative dielectric permittivity as the rock conditions changed from oil-wet to water-wet.