Electrical impedance variation with water saturation in rock

Abstract

We measured the electrical impedances of 22 sandstone samples during oil‐driving‐water tests using the two‐electrode method. Experiments show that the imaginary part X of the impedance (R + iX) of rock may respond well to water saturation in the frequency range 100 Hz–15 MHz. We found that the maximum −X values and their corresponding interfacial polarization frequencies are linear with water saturation. The lower critical frequency is found to vary with water saturation, in an unclear relationship with the characteristic length of rock. The dissipation factor at the interfacial polarization frequency remains quite stable and may be an indicator of the pore structure of rock. We used an equivalent circuit to explain the dispersive behavior of rock. More than one interfacial polarization frequency in the impedance Argand plot is predicted and can be observed if the measurement frequency range is wide enough.

Complex Electrical Measurements on an Undisturbed Soil Core: Evidence for Improved Estimation of Saturation Degree from Imaginary Conductivity

“…This weak dependence of σ″ on fluid chemistry has motivated the use of IP methods for improving lithologic discrimination relative to using resistivity alone (Weller et al, 2011; Weller and Slater, 2012; Weller et al, 2010). As previously discussed, σ″ typically exhibits a power law relationship with changes in saturation degree (Schmutz et al, 2010; Su et al, 2000): where a (S m −1 ) is a fitting parameter (Schmutz et al, 2010; Su et al, 2000; Ulrich and Slater, 2004). As mentioned before, Vinegar and Waxman (1984) proposed p = n − 1, based on the effects of oil as non‐wetting fluid in shaly sands.…”

Constitutive equations for ionic transport in porous shales

“…The ratio between the CEC and the specific surface area gives the equivalent total surface charge density of the mineral surface. Experimental data are from 1, Patchett [1975] (small solid circles, shales with >50 clays; open triangles, montmorillonite; large open circles, illite; open squares, kaolinite); 2, Lipsicas [1984] (solid triangles, Vermiculite); 3, Zundel and Siffert [1985] (large solid circles, illite; large solid squares, kaolinite; solid losange, chlorite); 4, Lockhart [1980] (inverted open triangles, kaolinite); 5, Sinitsyn et al [2000] (stars, illite); 6, Avena and De Pauli [1998] (grey solid circles: smectite); 7, Shainberg et al [1988] (small squares, smectite); 8, Su et al [2000] (crosses, shaly sands); and 9, Ma and Eggleton [1999, Table 3] (inverted solid triangles, kaolinite). The grey areas represent the domains of variations for kaolinite and chlorite, illite, and smectite.…”

Anisotropy of permeability and complex resistivity of tight sandstones subjected to hydrostatic pressure

“…This yields to a broadening of the dispersion which can often be described by the empirical Cole-Cole model (Cole and Cole, 1941). Although no theoretical model exists to explain experimental observations in detail, it is universally accepted that the interfacial polarization, characterized by relaxation time and dielectric dispersion, depends on the complex micro-geometry of the rocks or rather on the geometrical distribution and shape of the fluid-filled pores (Bona et al, 2002;Haslund, 1996;Hilfer, 1991;Lesmes and Morgan, 2001;Knight and Nur, 1987;Lysne, 1983;Ruffet et al, 1991;Sen, 1981;Su et al, 2000;Trukhan, 1963). Lysne (1983) derives from the Maxwell-Wagner-Sillars theory a model that relates the relaxation time τ to the geometric shape of a fluid inclusion, which is assumed to have a spherical form:…”