Fluid salinity, clay content, and permeability of rocks determined through complex resistivity partition fraction decomposition

Abstract

The types of physical mechanisms that generate induced electric polarization (IP) in rocks are here identified and their respective relaxation times are provided. Thus, the complex resistivity function associated with Dias’ model that describes the IP phenomenon is decomposed into partition fractions of an inverse third-degree polynomial in [Formula: see text]. Twelve rock samples’ data from the literature were used for this investigation. Using this procedure, two basic relaxations appear in the frequency range 1 mHz–1 MHz, where the phenomenon occurs. The first relaxation is associated with polarization caused by ionic diffusion proximal to the disseminated particle-electrolytic solution interfaces, which dominates in the low-frequency interval (approximately 1 mHz–100 Hz). The second process is capacitive-inductive polarization relaxation caused by an interaction between the electric double-layer capacitance and polarization-free pore resistances inside the polarization unit cell, which dominates in the high-frequency interval (approximately 10 kHz–1 MHz). At intermediate frequencies, these two processes combine to yield a transitional type of relaxation that dominates in the intermediate frequency interval (approximately 100 Hz–10 kHz). Our results, obtained using a given set of experimental data, provide a new method for determining the water salinity and clay content in the rock matrix without metallic particles. The rock permeability was also well determined by introducing Dias’ model parameter relationships and substituting the double-layer thickness for the grain size radius in a previously proposed formula.