Enhanced Electroseismic Coupling at Charged Interfaces

THOMPSON, A. H.; MONACHESI, L. B.; ZYSERMAN, F. I.; JOUNIAUX, L.

GEOPHYSICS

SOC EXPLORATION GEOPHYSICISTS

Año: 2023 p. 1 - 47

0016-8033

Published, field-scale studies of electroseismic (ES) surveying detected harmonics of thesource frequency in the detected seismic signal. At the time the data were collected, thecause of these high frequencies was unknown. We find that electric fields applied to lithologicalinterfaces create harmonics of the source frequency. At these interfaces, there aregradients in ionic concentrations in pore fluids and in situ electric fields associated withgradients in the electrochemical potential. When an electric field is applied to the junctionin the direction of the internal field, the internal voltage gradient decreases and theresistivity decreases. When the applied field opposes the internal field, the internal fieldincreases, and the resistivity is high. Harmonics of the applied AC field occur when theamplitude of the applied electric field is comparable to the internal field. We use thesandstone/limestone interface as an illustrative example. An analytical model of rock interfacespredicts the wavelet response to an applied field. The theoretically-predicted signalcharacteristics agree with the laboratory data. The model predicts that the distortion ofthe electric field induces strains on the rock matrix that are qualitatively similar to fieldmeasurements of ES conversion. The estimated response from an electrochemical junctionis substantially larger than electrokinetic conversion associated with displacement of thepore-surface dipole layers.