Three-dimensional nonlinear regularized inversion of the induced polarization data based on the Cole-Cole model

The quantitative interpretation of induced polarization (IP) data in a complex three-dimensional (3D) environment is a very challenging problem. The analysis of IP phenomena is usually based on models with frequency dependent conductivity distributions. In this paper, we develop a technique for 3D nonlinear inversion of IP data based on the Cole-Cole relaxation model. Our method takes into account, though in an approximate way, the nonlinearity of electromagnetic induction and IP phenomena, and inverts the observed data for the Cole-Cole model parameters. The solution of the 3D IP inverse problem is based on both smooth and focusing regularized inversion, which helps to generate more reliable images of the subsurface structures. The method is tested on synthetic models with anomalous conductivity and intrinsic chargeability, and is also applied to a practical 3D IP survey. We demonstrate that both the electrical conductivity and the chargeability distributions, as well as the other parameters of the Cole-Cole model, can be recovered from the observed IP data simultaneously. The recovered parameters of the Cole-Cole model can be used for the discrimination of the different types of mineralization, which is an important goal in mineral exploration.