Dielectric Constant Properties of Tight Sandstone

Abstract

This study stated dielectric properties of tight sandstone, which has porosity below 2%, and permeability below milli-Darcy. At this in-situs condition, the inter-pores are almost not connective, and throats are in micro-or nano-scale, so the electric conduction occupied weak position, but dielectric property predominated the current travelled through the rocks. Hence, the dielectric property is much significant characteristics should be investigated in order to better understand the electric mechanism of tight rocks. This paper illustrated the characteristics with experimental data from low to high frequency (Hz-kHz). Two parameters, resistivity and permittivity or dielectricity, were investigated with tight sandstone cores. The experiments were executed at room temperature (20˚C), the cores were injected into different content and salinity salt solution. The content, or say saturation of the solution in cores varied from 0-100% (in fact, completely salt solution) the salinity change from 0 (fresh water) to 1mg/mol. The experiment results showed that all of these two physical quantities, i.e. resistivity (R p ) and permittivity (Cp), have properties of frequency dispersion over the whole frequency range. Further analysis indicates that frequency dispersion of resistivity is relatively weak, but of dielectric, is much more obvious. That proved dielectric is more sensitive to saturation and salinity than resistivity, especially at low frequency. Two variables were introduced in order to describe the frequency dispersion properties D R and D C , which corresponded R p and C p respectively. D R and D C should indicate more detail account of the polarization and relaxation of components of tight sandstone cores, which will be further discussed in other paper.