Interpretation of Laboratory Measured Data: New Information on Pore Structure and Anisotropy using Relating to the IP Effect

Membrane polarization is a fundamental phenomenon of geophysical methods such as induced polarization (IP) method and frequency domain induced polarization method (FD IP). Determination of the characteristic parameters of induced polarization is required for studying physical properties of rocks. Mathematical modeling of a little known model of IP referred to as “induced polarization caused by constrictivity of pores” was conducted. Diffusion equations with specified boundary conditions that are different for current on- and off-times were used in the model. It was shown that membrane polarization occurs in all types of rocks if surface areas and transfer numbers are different for connected pores. During the polarization process all contacts between pores of different transfer numbers will be blocked and the electrical current will flow through the remaining canals. The new algorithm was tested on laboratory measurements. Several samples were selected: shale, mudstone, tillite, hematite, lava and manganese ore. Each theoretical model includes pores of more than 40 sizes sporadically distributed in the sample. The output of this stage of work is the pore size distribution in the sample, anisotropy and the relative amount of pores able to transport ions. It was shown that the size (pore radii) of pores can be different even when the porosity of samples is the same. The prevalent radii of investigated samples varied from 10 μm up to 1 μm. Laboratory data showed good agreement with theory and provided new information on the pore structure of rocks. Mathematical modeling provides reliable information of pores space of rocks, their dynamic porosity and permeability and transportation, especially of contaminant compounds