Experimental studies of seismoelectric conversions in fluid-saturated porous media

When seismic waves generate a relative fluid-solid motion in a fluid-satura ted porous medium, the moving charges (streaming current) in the electric d ouble layer induce an electromagnetic (EM) field. This paper first experime ntally confirms that the coupling between the seismic wave and the electrom agnetic field in the kilohertz range is electrokinetic in nature. Seismoele ctric signals are measured in homogeneous cylindrical porous rock samples a nd multilayered models. The seismoelectric signals in homogeneous rock are electric fields that move along with the acoustic wave. The mechanism of th e seismoelectric conversion is completely different from the piezoelectric effect of quarts grains. The seismoelectric sensitivity with respect to sal inity of the saturant has been experimentally determined. The amplitude of seismoelectric signals increases as the saturant conductivity decreases. Th e seismoelectric effects are generated by two different mechanisms. Both th e EM radiation and the electric potential generated at an interface and wit hin a porous medium, respectively, were measured as the P wave, at ultrason ic frequencies, passes through the layered models. Our experimental results demonstrate that seismoelectric effects exist and are measurable in the ki lohertz range. The paper concludes with a comparison of experimental data a nd modeled data in a three-layer porous model. Seismoelectric measurements could be an effective means of obtaining transport coefficients such as hyd raulic permeability and other porous rock properties.