You are here:
Influence of Oil Saturation Upon Spectral Induced Polarization of Oil Bearing Sands
Citation:
Schmutz, M., A. Revil, P. Vaudelet, M. Batzle, P. Vinao, AND D. D. WERKEMA. Influence of Oil Saturation Upon Spectral Induced Polarization of Oil Bearing Sands. JOURNAL OF GEOPHYSICAL RESEARCH. American Geophysical Union, Washington, DC, (183):211-224, (2011).
Impact/Purpose:
Induced polarization represents the measurement of the conductivity response (magnitude and phase) over a frequency range typically occurring from one milliHertz (sometimes down to the microhertz, see Olhoeft, 1985) to a few tens of kHz using at least two electrodes to inject electrical current and two electrodes to measured the resulting difference of electrical potential (Marshall & Madden, 1959; Olhoeft, 1986; Sturrock 1999; Lesmes & Morgan 2001; Slater & Lesmes 2002a). This method has been widely used also in the field, mainly qualitatively, for environmental purposes to investigate contaminant plumes (Olhoeft, 1986; Slater & Lesmes, 2002b) or to interpret downhole measurements in oil-bearing sediments (Vinegar & Waxman, 1982, 1984).
Description:
The presence of oil in an unconsolidated granular porous material such as sand changes both the resistivity of the material and the value of the phase shift between the low-frequency current and the voltage. The resistivity and the phase angle can be written as a complex-valued resistivity of the material. We performed laboratory experiments to investigate the influence of oil saturation (using a non-wetting oil), frequency (in the range 1 mHz-45 kHz), grain size, and conductivity of the pore water upon the complex resistivity response of an oil bearing sand. The low-frequency polarization (below 100 Hertz) is dominated by two effects: the polarization of the Stern layer (the inner part of the electrical double layer coating the surface of the grains in contact with water) with a small contribution from the Maxwell-Wagner polarization. In the frequency range 1 mH-100 Hz, the phase exhibits a well-defined relaxation peak with a peak frequency that is dependent on the mean grain diameter. Both the resistivity and the magnitude of the phase increase with the relative saturation of the oil. However because the phase depends on both the in-phase and quadrature conductivities, it may not be the parameter to model. The imaginary (quadrature) component of the complex conductivity is observed to decrease with the oil saturation. These results can be reproduced quantitatively with a grain polarization model that was initially developed by Revil and Florsch to model the relationship between induced polarization and permeability. Our results show this model can be extended to partial saturation conditions. It is also an improvement over previous model like the Vinegar and Waxman model, which do not account 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.