Seismoelectric effect: a non-isochoric streaming current. 1. Experiment

Propagation of ultrasound through a porous body saturated with liquid generates an electric response. This electroacoustic effect is called the "seismoelectric current"; the reverse process, when an electric field is the driving force, is called the "electroseismic current." Seismoelectric currents can be measured with electroacoustic devices originally designed for characterizing liquid dispersions. Such electroacoustic devices must first be calibrated with a liquid dispersion and then used to characterize a porous body. We demonstrated such measurements of the seismoelectric current with electroacoustic devices in three different types of porous bodies. The first porous body was a deposit of solid submicrometer particles. We monitored the kinetics of the deposit formation on the surface of the electroacoustic probe. It allowed us to unambiguously confirm that the measured signal was generated by the deposit. We were also able to extract information about the porosity of the forming deposits. The second type of porous body was again a deposit, but instead of solid submicrometer particles, we used very large, porous glass spheres. According to classical theory, these glass particles are not supposed to generate any electroacoustic signal because colloid vibration current decays with increasing particle size due to the particles inertia. Nevertheless, we measured a strong signal, which was apparently associated with the pores of the particles. We were able to derive some conclusions about the dependence of the seismoelectric current on the pore size. The last tests were performed with cylindrical sandstone cores. These porous bodies have a very high hydrodynamic resistance that prevents measurement of the classical streaming current. We are able to measure a strong seismoelectric current that correlates with porosity of the cores.