| Modeling induced polarization (IP) phenomena is important for developing effective methods for remote sensing of subsurface geology. Two resistivity relaxation models have been developed to describe the IP effect. The Cole-Cole model was formulated empirically more than 50 years ago. A few of the parameters within this model are able to account for IP phenomena and can give useful information for the analysis of bulk rock formations. Forward modeling using synthetic data is done to analyze the three empirical variables of the Cole-Cole model. These empirical variables are the decay coefficient (C), chargeability (m), and the time constant (tau). The generalized effective-medium theory of induced polarization (GEMTIP) model is another resistivity model similar to the Cole-Cole model. However, the GEMTIP model attempts to characterize heterogeneous, multiphase, polarized media using the effective-medium approach and can consider many more useful parameters than the Cole-Cole model. Forward modeling is also done with synthetic data to analyze four GEMTIP parameters. These parameters are the surface polarizability coefficient (alpha), the decay coefficient (C), the inclusion volume fraction (f), and the ellipticity of the inclusions (epsilon). Complex resistivity data was collected on several rock samples that contain disseminated sulfides, which are conducive to IP phenomena. Inversion of these data were done using both the spherical and elliptical GEMTIP models. In addition, complex resistivity data collected from a carbonate and two shale samples containing pyrite were also inverted using both the Cole-Cole and elliptical GEMTIP models in order to compare their effectiveness in recovering IP parameters. In the case of Cole-Cole inversion, the regularized Newton method was used, and in the case of GEMTIP inversion, the regularized conjugate-gradient method was implemented. Several of the parameters considered in this study were directly measured using X-ray microtomography and the QEMSCAN. Some of these parameters were included in the inversion routines to facilitate accurate inversion results.;While the exact cause of the IP effect is quite complicated and still not perfectly understood, it is known that being able to model it can be very useful in improving mineral discrimination techniques. With improved understanding of the IP effect and new advancements in rock physics models, mineral discrimination will become more effective as well as more reliable. |
