Effects of Wettability on Dielectric Properties of Porous Media

Abstract

Abstract We present in this paper the results of measurements of the complex dielectric permittivity and electric conductivity in oil-wet and water-wet porous media in a frequency range of 300kHz to 1.5GHZ. The porous media are made from unconsolidated acid-purified quartz sand which originally is water-wet. We used silylating agents to convert the same glass beads to hydrophobic oil-wetted surfaces. This avoided the effects of geometry on the dielectric permittivity that would happen if different glass grains are used. We have made measurements in a specially designed capillary pressure cell with a built-in transmission line which goes through the porous media. The measured capillary pressure curves serve as an indication of the degree of wettability. From the scattering characteristics of the built-in transmission line, we computed the complex dielectric permittivity of the porous media as function of frequency and water saturation We observed a significant difference in dielectric permittivity of water-wet and oil-wet porous media. At low water saturation, the dielectric permittivity of oil-wet sand is smaller than that of the water-wet one. At water saturation higher than 0.3, the dielectric permittivity of oil-wet sand becomes much larger that that of the water-wet one. Our results with results show the same trend observed by some previous researchers, but do not agree very well with dielectric permittivity, calculated using mixing models. This experimental study illustrates the importance of the wetting state of the porous media in determining their dielectric behavior.