Detecting electrical and hydraulic heterogeneities using seismic focusing and seismoelectric conversions

Abstract

When a seismic wave propagates through a porous material and encounters a discontinuity in hydraulic or electrical properties, part of its energy is converted into an electromagnetic signal. Recording and interpreting this signal can be used to infer properties of the subsurface such as electrical conductivity, porosity, permeability, and saturation. However, a major issue of this method is that the amplitude of the converted electromagnetic signal is usually quite low and difficult to measure directly in the field. Sava & Revil recently proposed a seismic focusing technique (which will be referred to as "beamforming"), where multiple seismic sources located around the area of interest (usually placed in boreholes) are used to concentrate seismic energy at a desired location and time. If the focus point is located at a heterogeneity, a seismoelectric conversion will take place with a much greater amplitude than if a unique source had been used, making the converted signal easier to detect. So far, this new technique has only been tested on a simple case study and further investigations are needed to assess its strengths, weaknesses, and future potential applications. In this thesis, I develop a finite-element numerical model for the beamforming technique (coupled with seismoelectric conversions) in the frequency domain. I then perform a set of important numerical tests to assess the properties of the converted electromagnetic signals generated by the beamforming technique. Finally, the numerical beamforming model is successfully applied to track the location of a water saturation front inside an oil reservoir undergoing a water flooding process.