Effects of Saturant Conductivity on Seismoelectric Conversion

Abstract

When a seismic wave propagates in a fluid-saturated porous medium, a seismoelectric field can be induced in the medium due to an electric double layer at the interface between solid and fluid. The strength of the seismoelectric field depends on the characteristics of the double layer and the conductivity of the saturant fluid. In our experiments two kinds of seismoelectric fields, a radiating electromagnetic (EM) wave and a localized electric field, are induced with fractured borehole models. The amplitudes of the seismoelectric signals are recorded when the conductivity of the saturant varies from zero to 27 mS/cm. The results show that when the conductivity increases, the amplitude of the electric signals increases at a low conductivity area and decreases at a high conductivity area. In this paper we investigate the mechanisms of seismoelectric conversion. When a double layer is saturated by charges in fluid, the amplitude of seismoelectric signals is inversely proportional to the conductivity. Conversely, if it is not saturated, the amplitude is directly proportional to the conductivity.