Seismoelectric Conversion in a Sample With Anisotropic Permeability

Because the porosity of natural rocks always is related to the permeability. The higher the porosity, the higher the permeability, and vice versa. It is difficult to distinguish the effects of the porosity and permeability on the seismoelectric conversion, because it is difficult to find two natural rock samples with the same porosity, but different permeability. In order to investigate the effect of rock permeability on the seismoelectric conversion, we create an artificial small porous cubic sample, whose sizes are less than the wavelength of the measurement acoustic wave. Because the micro fractures or pores spread unevenly inside the sample, the sample has anisotropic permeability in the different directions. Therefore, we can investigate the effect of the permeability on the seismoelectric conversion when the small sample has one value of porosity. In order to investigate the experimental error, two samples of Berea sandstone with the same sizes are made and the same seismoelectric measurements are conducted. If we suppose that the Berea sandstone samples are isotropic porous samples and the relative difference of the seismoelectric signals in the three directions are the experimental errors, the difference of the seismoelectric signals in the artificial sample is much larger than the experimental errors. We conclude that the seismoelectric conversion is related to the permeability of the porous sample.