Effect of surface polarization on resistivity modeling

Abstract

Spectral measurements of apparent resistivity show that serious errors may occur in scale modeling of resistivity with an electronic conductor immersed in an electrolyte unless the frequency of measurement is high enough to prevent the target-electrolyte interface impedance from affecting the observations. At lower frequencies the observed apparent resistivity is complex, and its magnitude neither represents the correct value nor obeys the scaling laws. Experiments demonstrate that the minimum safe frequency of measurement for acceptable resistivity modeling depends not only on the target and electrolyte material, but also on the shape, size, and relative disposition of the target and the measuring array. In some cases an operating frequency of 200 Hz may be adequately high; in others, 5000 Hz may be too low. The same considerations apply to the determination of "dilution factor" of a target by measuring apparent resistivities with two slightly different resistivity contrasts. With a solid conductor target the change in the observed apparent resistivity spectrum with a change of scale does not seem to follow any uniform scaling rule. This makes it difficult to model the apparent polarizability of a buried massive conductor target on a small scale.