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[1] 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.

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[1] This paper presents a novel pore-scale approach for the derivation of electrical properties of porous media. In this approach we create a digital porous medium on the basis of experimental grain-size distribution data and apply a drainage simulator based on pore-morphology analysis. Then we simulate via finite difference discretization the electrical charge flow within the two-fluid and solid porescale distributions, and derive the effective resistivity of the porous medium. Simulation results have been compared with resistivity data from a UK Permo-Triassic Sandstone (Sherwood S.). Agreement between measured and simulated bulk conductivities at different saturation values is excellent; this confirms the validity of the adopted approach, and its underlying assumptions.

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