Experimental studies of seismoelectric conversions in fluid-saturated porous media

Abstract

When seismic waves generate a relative fluid-solid motion in a fluid-saturated porous medium, the moving charges (streaming current) in the electric double layer induce an electromagnetic (EM) field. This paper first experimentally confirms that the coupling between the seismic wave and the electromagnetic field in the kilohertz range is electrokinetic in nature. Seismoelectric signals are measured in homogeneous cylindrical porous rock samples and multilayered models. The seismoelectric signals in homogeneous rock are electric fields that move along with the acoustic wave. The mechanism of the seismoelectric conversion is completely different from the piezoelectric effect of quartz grains. The seismoelectric sensitivity with respect to salinity of the saturant has been experimentally determined. The amplitude of seismoelectric signals increases as the saturant conductivity decreases. The seismoelectric effects are generated by two different mechanisms. Both the EM radiation and the electric potential generated at an interface and within a porous medium, respectively, were measured as the P wave, at ultrasonic frequencies, passes through the layered models. Our experimental results demonstrate that seismoelectric effects exist and are measurable in the kilohertz range. The paper concludes with a comparison of experimental data and modeled data in a three-layer porous model. Seismoelectric measurements could be an effective means of obtaining transport coefficients such as hydraulic permeability and other porous rock properties. Copyright 2000 by the American Geophysical Union.