The influence of temperature on the dielectric permittivity and complex electrical resistivity of porous media saturated with DNAPLs: A laboratory study

Abstract

While some recent studies have discussed various effects of temperature on the electric and electromagnetic properties of multiphase porous media, the effect of temperature changes in multiphase porous media polluted by dense non-aqueous phase liquids (DNAPLs) has rarely been documented. We attempted to characterize how relative permittivity and electrical resistivity vary with temperature in multiphase porous media. The measurements were carried out using two different column sizes. Glass beads with a 1 mm diameter were used to simulate porous media. Spectral induced polarization (SIP) and time domain reflectometry (TDR) were used to measure complex electrical resistivity and relative permittivity, respectively. We investigated the geophysical characteristics of two DNAPLs, coal tar (CT) and chlorinated solvent (CS), from 20 to 50 °C; ultra-pure water was used as the reference fluid. Experimental data on the relative permittivity and complex resistivity of pure water obey empirical models, validating our experimental setup and protocol. Results demonstrated that the real parts of relative permittivity and electrical resistivity are functions of temperature in the medium with the presence or absence of a solid phase. While we did not study the imaginary part of relative permittivity, our observations in the DNAPL samples indicated that temperature increases decreased the imaginary parts of the complex electrical resistivity of DNAPLs tested, whether in the presence or absence of the solid phase. Temperature dependency of relative permittivity and complex resistivity were also studied in multiphase porous media, after drainage (80% DNAPL and 20% water) and after imbibition (8% DNAPL and 92% water). The effect of temperature increases on complex resistivity has a secondary effect on frequency domain and Cole-Cole parameters. It was found that the relationship between temperature and resistivity is linear; therefore, resistivity temperature coefficients were obtained for water and both DNAPLs with the presence and absence of solid phase.