An analytical solution to assess theSHseismoelectric response of the vadose zone

Abstract

S U M M A R YWe derive an analytical solution of the seismoelectric conversions generated in the vadose zone, when this region is crossed by a pure shear horizontal (SH) wave. Seismoelectric conversions are induced by electrokinetic effects linked to relative motions between fluid and porous media. The considered model assumes a 1D soil constituted by a single layer on top of a half-space in contact at the water table, and a shearing force located at the earth's surface as the wave source. The water table is an interface expected to induce a seismoelectric interfacial response (IR). The top layer represents a porous rock in which porous space is partially saturated by water and air, while the half-space is completely saturated with water, representing the saturated zone. The analytical expressions for the coseismic fields and the interface responses, both electric and magnetic, are derived by solving Pride's equations with proper boundary conditions. An approximate analytical expression of the solution is also obtained, which is very simple and applicable in a fairly broad set of situations. Hypothetical scenarios are proposed to study and analyse the dependence of the electromagnetic fields on various parameters of the medium. An analysis of the approximate solution is also made together with a comparison to the exact solution. The main result of the present analysis is that the amplitude of the interface response generated at the water table is found to be proportional to the jump in the electric current density, which in turn depends on the saturation contrast, poro-mechanical and electrical properties of the medium and on the amplitude of the solid displacement produced by the source. This result is in agreement with the one numerically obtained by the authors, which has been published in a recent work. We also predict the existence of an interface response located at the surface, and that the electric interface response is several orders of magnitude bigger than the electric coseismic field, whereas it is the opposite using compressional waves as shown by theoretical and experimental results. This fact should encourage the performance of field and laboratory tests to check the viability of SHTE seismoelectrics as a near surface prospecting/monitoring tool.

Water Table and Permeability Estimation From Multi‐Channel Seismoelectric Spectral Ratios

“…The SE method can be used to determine hydrogeological properties provided the data measured on the ground surface or in boreholes are properly interpreted (Revil et al., 2012). During the past two decades, the SE method has seen significant development through (a) theoretical studies (e.g., Huang, 2002; Jougnot & Solazzi, 2021; Monachesi et al., 2018; Solazzi et al., 2022; Thanh et al., 2022), (b) numerical modeling approaches (e.g., Garambois & Dietrich, 2002; Grobbe & Slob, 2016; Haines & Pride, 2006; Hu & Gao, 2011; Jougnot et al., 2013; Ren et al., 2016a, 2016b; Zheng et al., 2021), (c) physical laboratory experiments (e.g., Bordes et al., 2015; Devis et al., 2018; Wang et al., 2020; Zhu & Toksöz, 2013), and (d) field measurements (e.g., Butler et al., 2018; Dupuis & Butler, 2006; Garambois & Dietrich, 2001; Rabbel et al., 2020; Thompson & Gist, 1993). As the understanding of SE signals grows, this method is of increasing interest to researchers in near‐surface geophysics (e.g., Grobbe et al., 2020).…”

Modeling the Frequency‐Dependent Effective Excess Charge Density in Partially Saturated Porous Media

“…Given its inherent sensitivity to flow dynamics and pore fluid characteristics, the seismoelectric method can provide highly valuable information for studying this type of environments (Grobbe et al., 2020; Revil et al., 2015). The physical principles upon which seismoelectric prospecting is based on have been used in context of groundwater management and remediation (e.g., Dupuis et al., 2007; Han et al., 2004; Monachesi et al., 2018), exploration and production of hydrocarbons (e.g., Revil & Jardani, 2010), and CO 2 geosequestration operations (e.g., Zyserman et al., 2015). Novel approaches addressing the complex processes behind the seismic‐to‐electric conversion are of great interest, as they may help to better interpret seismoelectrical signatures in partially saturated environments.…”

Transport in Porous Media Electromagnetic/acoustic coupling in partially-saturated porous rocks: An extension of Pride's theory --Manuscript Draft-- Manuscript Number: TIPM-D-22-00221 Full Title: Electromagnetic/acoustic coupling in partially-saturated porous rocks: An extension of Pride's theory

“…Laboratory experiments were performed by Bordes et al (2015) on the seismoelectric response of partially saturated sand using effective fluids in the associated computations of transfer functions. Another model was proposed by Jardani and Revil (2015) overlying a fully saturated one was published by Monachesi et al (2018). More recently passive electromagnetic sources have been considered by Zyserman et al (2022) to study the seismic responses of a hydrocarbon reservoir at different oil saturations.…”