E ects of Saturant Conductivity on Seismoelectric Conversion

When a seismic wave propagates in a uid-saturated porous medium, a seismoelectric eld can be induced in the medium due to an electric double layer at the interface between solid and uid. The strength of the seismoelectric eld depends on the characteristics of the double layer and the conductivity of the saturant uid. In our experiments two kinds of seismoelectric elds, a radiating electromagnetic (EM) wave and a localized electric eld, 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 uid, 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.