Enhanced Electroseismic Coupling at Charged Interfaces

THOMPSON, ARTHUR; LEONARDO MONACHESI; ZYSERMAN, F I; JOUNIAUX, L

GEOPHYSICS

SOC EXPLORATION GEOPHYSICISTS

Lugar: Tulsa, OK; Año: 2023

0016-8033

Published, field-scale studies of electroseismic (ES) surveying detected harmonics of the sourcefrequency in the detected seismic signal. At the time the data were collected, the cause ofthese high frequencies was unknown. We find that electric fields applied to lithological interfaces create harmonics of the source frequency. At these interfaces, there are gradients in ionicconcentrations in pore fluids and in situ electric fields associated with gradients in the electrochemical potential. When an electric field is applied to the junction in the direction of the internal field, the internal voltage gradient decreases andthe resistivity decreases. When the applied field opposes the internal field, the internal field increases, and the resistivity is high. Harmonics of the applied AC field occur when the amplitude of the applied electric field is comparable to the internal field. We use the sandstone/limestone interface as an illustrative example. An analytical model of rock interfaces predicts the wavelet response to an applied field. The theoretically-predicted signal characteristics agree with the laboratory data. The model predicts that the distortion of the electric field induces strains on the rock matrix that are qualitatively similar to field measurements of ES conversion. The estimated response from an electrochemical junction is substantially larger than electrokinetic conversion associated with displacement of the pore-surface dipole layers.