An analytical study of seismoelectric signals produced by 1D mesoscopic heterogeneities

TL;DR

This study provides an analytical framework to understand how mesoscopic heterogeneities in fluid-saturated rocks influence seismoelectric signals, revealing dependencies on petrophysical properties and potential for subsurface characterization.

Contribution

The paper introduces an analytical solution for seismoelectric response in rocks with mesoscopic heterogeneities, including fractures, and analyzes parameter impacts on signals.

Findings

Seismoelectric signal amplitude is proportional to applied stress and material contrasts.

Maximum electrical potential frequency depends on permeability and thickness of less permeable regions.

Seismoelectric measurements can estimate rock properties like permeability and fracture compliance.

Abstract

The presence of mesoscopic heterogeneities in fluid-saturated porous rocks can produce measurable seismoelectric signals due to wave-induced fluid flow between regions of differing compressibility. The dependence of these signals on the petrophysical and structural characteristics of the probed rock mass remains largely unexplored. In this work, we derive an analytical solution to describe the seismoelectric response of a rock sample, containing a horizontal layer at its center, that is subjected to an oscillatory compressibility test. We then adapt this general solution to compute the seismoelectric signature of a particular case related to a sample that is permeated by a horizontal fracture located at its center. Analyses of the general and particular solutions are performed to study the impact of different petrophysical and structural parameters on the seismoelectric response. We find that the amplitude of the seismoelectric signal is directly proportional to the applied stress, to the Skempton coefficient contrast between the host rock and the layer, and to a weighted average of the effective excess charge of the two materials. Our results also demonstrate that the frequency at which the maximum electrical potential amplitude prevails does not depend on the applied stress or the Skempton coefficient contrast. In presence of strong permeability variations, this frequency is rather controlled by the permeability and thickness of the less permeable material. The results of this study thus indicate that seismoelectric measurements can potentially be used to estimate key mechanical and hydraulic rock properties of mesoscopic heterogeneities, such as compressibility, permeability, and fracture compliance.