Theoretic analysis and experimental investigation of induced polarization effect of rocks/minerals

This paper considers the polarization phenomena and measurement techniques of rock materials in the view of system identification and parameter estimation. Induced Polarization method is used to measure the rock materials, which is a scheme for using electric fields in the earth to estimate physical structure. These fields are generated by the deliberate injection of electrical currents into the earth. The effective conductivity of rock materials for alternating current is not in general constant, but is variable and complex. The complex conductivity in the frequency domain gives rise to the overvoltage or induced polarization effect in the transient time domain. Usually traditional Cole-Cole model is used to describe the conductivity of rock materials in the frequency domain. But practical measuring data in the frequency domain proves that Cole-Cole model is not the best description of the characteristics of the polarization phenomena of rock materials. Also it is difficult to discriminate between a valid induced polarization (IP) response and electromagnetic (EM) coupling effects, which are caused by IP measurement and the complexity of the rock materials. Therefore we use a system identification method to find an adequate IP system model. Summarizing the analysis of the IP system model, it is concluded that the proposed IP system model fits the field data much better than the traditional Cole-Cole model. EM coupling effects can be removed using system identification method and the induced polarization effect in the transient time domain can be presented in Simulink via the IP system model.