Salinity dependence of spectral induced polarization in sands and sandstones

Abstract

International audienceIn electrolyte-saturated sands, the reversible storage of electrical charges is responsible for a phase lag between the current (injected and retrieved by two current electrodes) and the electrical field recorded by two voltage electrodes. This phenomenon is called 'spectral induced polarization' in geophysics and can potentially be used to monitor salt tracer tests in shallow aquifers to infer their permeability and dispersivity tensors. We demonstrate analytically that the polarization of the inner part of the electrical triple layer coating the surface of the grains (named the Stern layer in electrochemistry) is consistent with available data. We also perform new experiments using silica sands saturated by NaCl and CaCl2 pore water solutions. The salinity dependence of quadrature conductivity can be modelled using an analytical solution of the triple layer model, which offers a simple way to interpret laboratory and field data. This analytical solution depends on the total site density of the mineral surface, the pH value and the sorption coefficient of the cation in the Stern layer. This model shows that both the specific surface conductivity of the Stern layer and the quadrature conductivity of the porous material depend on the conductivity of the pore water. The quadrature conductivity is becoming independent of the salinity above 1 S m−1. The parameters entering the analytical model are consistent with independent estimates from titration data and zeta potential measurements, which are two classical methods to characterize the electrical triple layer at the pore water mineral interface

Quadrature conductivity: A quantitative indicator of bacterial abundance in porous media

“…Only the current electrodes would display polarization because of the change of the nature of the charge carriers at their surface (Kemna, 2000). Several benchmark tests of the impedance meter used in this study can be found in Revil and Skold (2011). The complex conductivity response obtained with water alone, as expected, does not display polarization effects (see Figure 5 of Revil and Skold, 2011).…”

“…The second term of equation 2 corresponds to the conductivity of the bacteria themselves (the surface conductivity of the bacteria σ S B 0 and the conductivity of a single bacterium is given by σ B ¼ ð1 − fÞ β ðþÞ ρ B CEC B ) (Revil et al, 2012a). Note that alternatively, we could express the conductivity of a bacterium in terms of its radius and its surface conductance produced by the diffuse layer (see, for instance, Revil and Skold [2011] for sand grains). Both approaches are valid, but the CEC is usually the reported parameter describing the electrochemical properties of the bacteria surface, not the surface conductance.…”

“…The accuracy on the phase is 0.1 mrad below 100 Hz (Zimmermann et al, 2008). The data acquisition system can operate in the frequency range from 1 mHz to 45 kHz with a phase accuracy of 0.1 mrad below 100 Hz (see Revil and Skold [2011] for various benchmark tests, including tests performed with electric circuits with a known resistance in parallel with a known capacitance).…”

“…Several benchmark tests of the impedance meter used in this study can be found in Revil and Skold (2011). The complex conductivity response obtained with water alone, as expected, does not display polarization effects (see Figure 5 of Revil and Skold, 2011). The SIP measurements for the Z. mobilis experiments were taken using the ZEL-SIP04-V02 impedance meter (Zimmermann et al [2008], Figure 6c).…”

Seawater capacitance – a promising proxy for mapping and characterizing drifting hydrocarbon plumes in the deep ocean

“…3), and multi-viscosity oil was titrated into it and stirred to force dissemination. Experiments with conductive fluids in sandstones indicate that any phase shift is independent of the fluid conductivity (Revil and Skold, 2011).…”