Influence of oil saturation upon spectral induced polarization of oil-bearing sands

M. Schmutz,A. Revil,P. Femenía Viñao,M. Batzle,P. Vaudelet,D. D. Werkema

doi:10.1111/j.1365-246x.2010.04751.x

Abstract

SUMMARY The induced polarization model developed recently by Revil and Florsch to understand the complex conductivity of fully saturated granular materials has been extended to partial saturation conditions. It is an improvement over previous models like the Vinegar and Waxman model, which do not account explicitly for the effect of frequency. The Vinegar and Waxman model can be considered as a limiting case of the Revil and Florsch model in the limit where the distribution of relaxation times is very broad. The extended model is applied to the case of unconsolidated sands partially saturated with oil and water. Laboratory experiments were performed to investigate the influence of oil saturation, frequency, grain size, and conductivity of the pore water upon the complex resistivity response of oil-bearing sands. The low-frequency polarization (below 100 Hz) is dominated by the polarization of the Stern layer (the inner part of the electrical double layer coating the surface of the grains in contact with water). The phase exhibits a well-defined relaxation peak with a peak frequency that is dependent on the mean grain diameter as predicted by the model. Both the resistivity and the magnitude of the phase increase with the relative saturation of the oil. The imaginary (quadrature) component of the complex conductivity is observed to decrease with the oil saturation. All these observations are reproduced by the new model.

Highlights

Induced polarization represents the measurement of the conductivity response over a frequency range typically occurring from 1 mH to a few tens of kilohertz
5 CONCLUDING STATEMENTS We have performed spectral induced polarization measurements with fresh oil-bearing sands investigating the influence of different parameters including (1) the oil saturation, (2) the conductivity of the pore water, and (3) the mean grain diameter of the sand
Our goal was to extend and to further test the spectral induced polarization model developed recently by Revil & Florsch (2010). This model is based on the polarization of the Stern layer at the sand/water interface and the polarization length scale is the size of the grains because of the discontinuity of the Stern layer between grains

Summary

Introduction

Induced polarization represents the measurement of the conductivity response (magnitude and phase) over a frequency range typically occurring from 1 mH (sometimes down to the microhertz, see Olhoeft 1985) to a few tens of kilohertz. Vanhala et al (1992) described the spectral induced polarization signature associated with the presence of toluene, heptane, and ethylene glycol in glacial tills. They observed an increase of the magnitude of the phase in the presence of these organic contaminants. Cassiani et al (2009) performed an investigation showing the effect of the saturation in hydrocarbons upon induced polarization (using a NW oil) but they investigated only few extreme values in the oil saturation They were able to fit their data with the empirical Cole–Cole model but this empirical relationship does not explain the experimental results from a mechanistic standpoint

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Conclusion