Integrated dielectric model for unconsolidated porous media containing hydrate

This article reports a novel dielectric model developed for estimating the complex permittivity of unconsolidated porous media containing gas hydrate. The complex permittivity spectra were experimentally obtained by using open-ended-coaxial-probes over a frequency range between 1 MHz and 3 GHz, in which the dielectric dispersion of both hydrate and liquid solution are covered. With tetrahydrofuran used as the hydrate former, reflection coefficients were recorded during the hydrate formation and dissociation processes in quartz sands and the complex permittivity spectra were inversed. Volumetric fractions estimated from the X-ray-tomography were used as the referenced values. Experimental data showed that the Maxwell-Wagner effect, surface conductance, and phase configuration can affect the bulk permittivity. The discrepancy was found to be unacceptable when the fitting was conducted with pre-existing models such as complex-refractive-index-method (CRIM) and Maxwell-Wagner-Bruggeman-Hanai (MWBH). In this study, by modifying the nested Wagner's theory, a shell-coated model was applied, and the surface of the solid sphere was assumed to possess surface conductance when it was humidified by the liquid solution. In contrast to CRIM and MWBH, the proposed model allows more accurate estimation of the volumetric fraction. By adopting this model with a range of dielectric measurements with different phase configurations, temperature, particle size, surface conductivity, and frequency, the contents of components and their influences onto the bulk permittivity can be physically estimated. The proposed model provides an essential tool for the interpretation of dielectric dispersion curves and the prediction of the volumetric fractions, which can be useful for both the field and laboratory applications.