Spectral IP studies on buried scale models incorporating surface and volume polarisation

Abstract

Spectral measurements of apparent resistivity and phase shift using a two electrode array or a Wenner electrode array over a cement-graphite sheet model immersed in an electrolyte (i.e. volume polarisation), reveal that the frequency of maximum phase shift, Fm, varies with the array geometry and its disposition with respect to the target model. In the authors' opinion, this suggests that practical mineral discrimination by measurement of spectral IP may only be a remote possibility. However, the Fm, for a given electrode array, is much smaller for a metallic model of the same dimensions, immersed in the same electrolyte. This means that in order to do accurate resistivity modelling, the excitation current frequency needed is much less than that is required in the case of the metallic model under the same conditions. The model tank apparent resistivity responses over the cement-graphite model sheet measured with time domain IP equipment very much resemble the corresponding resistivity responses obtained over a metallic model of the same dimensions under similar conditions. Practising geophysicists should keep this result in mind when interpreting IP field data.