Spectral induced polarization of partially saturated clay-rocks: a mechanistic approach

Abstract

International audienceWe have developed a mechanistic model to interpret spectral induced polarization data of partially saturated clay-rocks. This model accounts for the polarization of the grains through an electrical double layer model with a polarization model of the inner part of the electrical double layer called the Stern layer. The polarization model accounts also for the Maxwell-Wagner polarization at frequencies higher than 100 Hz. The Maxwell-Wagner polarization is modelled by using a conductivity model modified to account for the presence of a non-wetting immiscible phase like air in the pore space. The resulting model is consistent with the first and second Archie's laws in the case where surface conductivity can be neglected. The volumetric charge density of the diffuse layer at saturation is divided by the saturation of the water phase to account for the partial water saturation of the porous material. The model comprises seven fundamental parameters: the formation factor, the second Archie's exponent, a critical water saturation level, the mean electrical potential of the pore space at saturation, the density of the counterions in the Stern layer, and at least two parameters describing the grain size distribution. Most of these parameters can be derived independently using alternative measurements and electrochemical models. Measurements were performed in the frequency range 10 mHz-45 kHz using five samples from the Callovo-Oxfordian formation in the eastern part of the Paris Basin, France. The model agrees fairly well with the experimental data at saturation and for partially saturated clay-rocks down to 1 Hz. Most of the seven physical parameters entering the model were independently evaluated

Dependence of spectral‐induced polarization response of sandstone on temperature and its relevance to permeability estimation

“…In various studies it has been found that the ionic mobility of the counterion species in the Stern and diffuse layers is close to the mobility of this species in the bulk pore electrolytic solution b + f [e.g., Tarasov and Titov, 2007;Leroy et al, 2008]. This can be explained by the location of the counterion on the outer Helmholtz plane of the Stern layer, where it keeps its hydration shell [Tournassat et al, 2009;Jougnot et al, 2010;Revil and Florsch, 2010]. This might be different for counterion species with a higher affinity to the mineral surface and for minerals with permanent structural charges on their basal surface (e.g., illite and smectite) [Leroy and Revil, 2009].…”

“…Leroy and Revil [2009] mention that membrane polarization might make a significant contribution to effective polarization at low frequencies (f < 1 Hz), at least in clays. Nevertheless, as demonstrated in various publications, the SIP response of sands and clays can be modeled from EC mechanisms without requiring any flush factor [e.g., Leroy et al, 2008;Leroy and Revil, 2009;Jougnot et al, 2010;Revil and Florsch, 2010]. We assume, therefore, that EC polarization makes the dominant contribution to the effective polarization occurring in sandstones in the investigated frequency range.…”

“…Also, we assume full water saturation. The dependence of EC polarization response on saturation is discussed by Jougnot et al [2010].…”

Complex conductivity of soils

“…The imposed injection voltage is set to 1 V. The measured phase is typically below 50 mrad, and most of the cases below 10 mrad imposing the use of very rigorous procedures including (1) the use of 4 electrodes configuration, (2) electrodes with small phase errors and input impedances, (3) the minimization of potential electromagnetic couplings at high frequencies (i.e., minimizing metallic parts in the sample holders), (4) very stable electrodes for the low frequency measurements (i.e., no drifts), and (5) a correction procedure for equivalent circuit of the system without the core samples. The phase accuracy is typically around 0.1-0.2 mrad below An important point in the evaluation of the electrical conductivity is the determination of the geometrical factor (or cell constant) of the sample holder (e.g., Jougnot et al [2010]). …”

Modeling the evolution of complex conductivity during calcite precipitation on glass beads

“…the reversible storage of electrical charges) of porous materials (Kemna et al 2012). Polarization of oxides and carbonates minerals such as calcite is related to the polarization of the electrical double layer (EDL) surrounding the particles under an external alternating current or electrical field (Chelidze & Gueguen 1999;Jougnot et al 2010;Revil & Florsch 2010). When a sinusoidal current at a range of frequencies is applied to the charged porous medium and the resulting difference of electrical potential is measured, complex conductivity is referred to as spectral induced 124 P. Leroy et al polarization (SIP) (Collet 1990;Weller & Borner 1996;Luo & Zhang 1998;Huisman et al 2015).…”