Interfacial polarization of disseminated conductive minerals in absence of redox-active species — Part 2: Effective electrical conductivity and dielectric permittivity

Abstract

Hydrocarbon-bearing conventional formations, mudrock formations, and source-rock formations generally contain clays, pyrite, magnetite, graphitelike carbon, and/or other electrically conductive mineral inclusions. Under redox-inactive conditions, these inclusions give rise to perfectly polarized interfacial polarization (PPIP) when subjected to an external electric field. Effective electrical conductivity and dielectric permittivity of geomaterials containing such inclusions are frequency-dependent properties due to the electric-field-induced interfacial polarization and associated charge relaxation around host-inclusion interfaces. Existing resistivity interpretation techniques do not account for PPIP phenomena, and hence they can lead to inaccurate estimation of water saturation, total organic content, and conductivity of formation water based on subsurface galvanic resistivity, electromagnetic (EM) induction, and EM propagation measurements in the presence of conductive mineral inclusions. In the first paper of our two-part publication series, we derived a mechanistic electrochemical model, the PPIP model, and we validated a coupled model that integrates the PPIP model with a surface-conductance-assisted interfacial polarization (SCAIP) model to quantify the frequency-dependent electrical complex conductivity of geomaterials. We have used the PPIP-SCAIP model to evaluate the dependence of effective complex-valued conductivity of geologic mixtures on (1) frequency, (2) conductivity of the host medium, and (3) material, size, and the shape of inclusions. Notably, we have used the PPIP-SCAIP model to identify rock conditions that give rise to significant differences in effective conductivity and effective relative permittivity of conductive-inclusion-bearing mixtures from those of conductive-inclusion-free homogeneous media. For a mixture containing as low as a 5% volume fraction of disseminated conductive inclusions, the low-frequency effective conductivity of the mixture is in the range of [Formula: see text] to [Formula: see text] with respect to the host conductivity for frequencies between 100 Hz and 100 kHz. Further, the high-frequency effective relative permittivity of that mixture is in the range of [Formula: see text] to [Formula: see text] with respect to the host relative permittivity for frequencies between 100 kHz and 10 MHz.