Electrical properties of partially saturated sandstones: Novel computational approach with hydrogeophysical applications

Electric and electromagnetic geophysical tools are suitable methods for investigating moisture content, transport, and storage properties of the subsoil with noninvasive surveys. Interpretation of field data is still based on empirical or semiempirical equations, which must be calibrated with complex, time-consuming laboratory measurements. In this paper we develop pore-scale models suitable for computing the effective electric conductivity and the effective permittivity of partially saturated porous media on the basis of simple structural parameters ( grain size distribution and porosity). We compute the electrical conductivity with three approaches that model the conductivity of the shell of coating clay around solid grains of shaly sandstones using different assumptions. We compare the simulated results with experimental data from Sherwood Sandstone (UK) and discuss the effect of these assumptions on the effective conductivity. Simulations performed using a modeling approach that accounts for interaction between volume and surface conduction show an excellent agreement with experimental data. We also model the effective permittivity of the same porous medium at several saturation values and obtain a good match with laboratory measurements.