The Effect of Rock Permeability and Porosity on Seismoelectric Conversion

Abstract

The seismoelectric coupling coefficient indicates the strength of seismoelectric conversion. In our study, an experimental apparatus was designed to record the seismoelectric signals induced in water-saturated sandstones in the frequency range from 10K to 500 KHz. The results were interpreted using a micro-capillary model for the porous medium to describe the seismoelectric coupling. The relationship between seismoelectric coupling coefficients and the permeability and porosity of sandstones were also examined theoretically. A general agreement between the theory and the test data indicates that seismoelectric conversion is enhanced by increases in porosity over a range of different frequencies. However, seismoelectric conversion has a complex relationship with rock permeability, that changes with frequency. In the low frequency range (0-50KHz), seismoelectric coupling strengthens with the increase of permeability logarithmically. In the high frequency range (50K-10000KHz), the seismoelectric coupling is at first enhanced, with small increases of permeability leading to small increases in seismoelectric coupling. However, continued increases of permeability lead to a slight decrease in size and image conversion again. The experimental and theoretical results indicate that seismoelectric conversion seems to be more sensitive to the changes of low-permeability samples. This suggests that seismic conversion may have advantages in characterizing low permeability reservoirs.