ABSTRACT

Streaming potentials can be generated when geologic porous media are subjected to pumping tests. For a homogeneous medium, theory predicts that input and output points for water circulation generate field responses in the form of electric potentials that are equivalent to those produced by current sources that are externally driven by a power source. We evaluated tank experiments showing that this assumption is valid for common geophysical scenarios and can be used to determine charge density for porous geologic media, a key parameter in interpreting electrokinetic and interfacial properties in hydrogeophysics. We also determined that when water circulation encompasses a heterogeneity, the equivalence with single current poles is lost, and this can be used as a field criterion to detect inhomogeneities near a well. Our experimental results were analyzed with finite-element modeling of water and charge flow, showing that an interfacial distribution of currents must be expected as the cause of distortions in self-potential fields. We developed a procedure that used the background resistivity model to better image the distribution of currents onto media interfaces, pointing out advances still needed and challenges still remaining to improve source imaging.

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