Detection of non-aqueous phase liquid contamination by SH-TE seismoelectrics: A computational feasibility study

Abstract

In this work we propose a one dimensional numerical study of the seismoelectric signals produced in a fresh water aquifer contaminated by either light or dense non-aqueous phase liquids ((L/D)NAPLs), considering a pure SH-wave seismic source. We investigate the nature of the electromagnetic response generated at media interfaces, the so called Interface Response (IR), by comparing it with the electromagnetic field generated by a current sheet; wherefrom we are able to interpret that the source of the IR behaves as an electric current flowing along the interface, differently to what happens when the IR is originated by the action of a P-wave, where electric charge accumulation generates an electric dipole. We perform a parametric study to analyze how the presence of contaminants affects the IR, resorting to an effective media approach to compute mechanical and electromagnetic properties, and considering three different effective fluid-saturation dependent electrokinetic coupling coefficient models. We observe, as expected, that porosity plays an important role in the amplitude of the IRs. When considering different NAPL saturations, significant effects on the IRs are only seen when the thickness of the contaminated layer is above a threshold value, which depends on the present contaminant and the considered effective electrokinetic coupling coefficient model.