Induced polarization of clay-rich materials — Part 1: The effect of desiccation

Abstract

A petrophysical model describing spectral induced polarization has been developed for clay-rocks accounting for the Maxwell Wagner polarization. It is also used to connect the complex conductivity to the relative permeability of the material. This model is applied to the Callovo-Oxfordian (COx) clay-rock of the Paris Basin (France) where the Meuse/Haute-Marne Underground Research Laboratory (URL) is located. Laboratory experiments are performed using 8 clay-rock cores to study the effect of desiccation on their spectral induced polarization response. The measurements are performed along the foliation plane. Complex conductivity spectra are performed over the frequency range 1 mHz to 45 kHz. These spectra are fitted with a double Cole Cole model to extract the evolution of the Cole Cole parameters with the saturation during the desiccation process. The low-frequency Cole Cole model corresponds to induced polarization phenomena while the high-frequency Cole Cole model corresponds to the Maxwell-Wagner contribution. We obtain the value of the first and second Archie’s exponents and we check the relationship between the surface conductivity and the cation exchange capacity of the clay-rocks. We are also able to connect the relative permeability curve to the second (saturation) Archie’s exponent. The monitoring of the complex conductivity can be used to predict how the permeability of the clay-rock formation changes with the water content.

Induced polarization of clay-rich materials — Part 2: The effect of anisotropy

“…In Equation ( 5), r k denotes the relative permeability of the rock and  is a hydraulic pore radius. As discussed in Revil et al (2023), the relative permeability is given by, 2 ()…”

“…If the function EV extracts the eigenvalues of a given tensor, then we have s  denotes the irreducible water saturation for the COx as obtained in the previous paper of this series (Revil et al, 2023).…”

“…We observe that both the amplitude of the conductivity and quadrature conductivity decrease with the saturation. For these experiments, we use exactly the same experimental protocol and sample holder as in Revil et al (2017a) so the details of the experiments will not be repeated here (see also Revil et al, 2023). The complex conductivity spectra are fitted with a double Cole Cole model (see Appendix A).…”

Organic Matter Matters—The Imaginary Conductivity of Sediments Rich in Solid Organic Carbon

“…Electrochemical polarization models for mineral sediments are based on surface complexation models that estimate the surface conductivity in the Stern and diffuse layers of the EDL (Leroy & Revil, 2009; Leroy et al., 2008; Revil & Skold, 2011). They yield a linear relationship between σ ″ and the surface site density, Γ s [sites m −2 ], which can be determined from the cation exchange capacity (CEC) [mmol charge g sed −1 ] and surface area, A surf [m 2 g sed −1 ], using: $$${{\Gamma }}_{\mathrm{s}}=\frac{\text{CEC}}{{A}_{\text{surf}}}$$$ so that the CEC, a comparatively easy to acquire bulk property of sediments, can reliably predict the polarizability of a sediment (Revil et al., 2023).…”

“…(2) so that the CEC, a comparatively easy to acquire bulk property of sediments, can reliably predict the polarizability of a sediment (Revil et al, 2023).…”