A novel analysis of the electrical transport mechanisms in porous media

Effects of water saturation and wettability on the dielectric constant are investigated experimentally using four-electrode impedance measurements, an d theoretically using models that account for the electrical double layer p olarization. Complex impedance measurements, performed on Berea sandstone a nd on Ottawa-sand packs in the frequency range 10 Hz to 1 MHz, appear to in dicate that the dielectric constant varies linearly with water saturations above 50%. The rate of change of dielectric constant with saturation is fou nd to be a function of frequency. As the frequency increases this rate of c hange decreases. The decrease in the slope of the dielectric constant-water saturation profile with frequency is not intuitively obvious, but has been proven theoretically in this work. The dielectric constant of water-wet sa mples is found higher than that of the oil-wet samples at all water saturat ions. The difference is more pronounced at high water saturations near unit y. The wettability changes have been simulated using a generalized Maxwell- Wagner model by varying the amount of ionic surface charge of rocks. In gen eral oil-wetting agents react with the formation matrix by connecting their positively charged tails to the negatively charged silica surfaces, loweri ng the surface charge density. Simulations show that the effect of wettabil ity changes on the dielectric constant is very significant. These conclusio ns are consistent with the experimental results presented in this study.