Abstract

Archie's Law for the porosity and saturation dependence of electrical conductivity, σ(ϴ) = aσbϕm(ϴ/ϕ)n (where σ is electrical conductivity, the subscript b denotes the brine or bulk solution, ϕ is porosity, ϴ is volume wetness, and a, m, and n are fitting parameters) was recently derived by applying continuum percolation theory to fractal porous media. We have recast Archie's Law in terms of saturation alone to obtain σ(ϴ) = σ0 (ϴ − ϴc)μ, where ϴc is the critical volume fraction for percolation, and σ0 = aσb/(1 − ϴc)μ. The value of the exponent, μ = 2.0 for three-dimensional systems and 1.28 for two, is consistent with theory and simulations. We examined the universality of the exponent's value, and the range of validity of our expression. Drawing on published data, we compared predicted and measured values of σ(ϴ) across the full range of saturation, and found that the newly derived expression provides good predictions, is robust with respect to secondary effects such as residual salinity and contact resistance, and yields meaningful physical parameters.

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