Coaxial method to investigate broadband dielectric properties of rocks over the 5 Hz to 3 GHz frequency range

In this paper, we present a novel approach to study the electrical properties of intact rock by combining impedance and vector network analyzer measurements in the frequency range from 5 Hz to 3 GHz. For the first time, this study enables electrical characterization of the exact same rock sample over nine orders of magnitude in frequency range, utilizing a coaxial cell apparatus with specifically prepared rock samples. Three types of rocks (basalt, sandstone and granite) with low to intermediate porosity (12.24%, 16.9% and 7.49%, respectively) were characterized at varying saturation levels. The relaxation behavior of the samples was quantified using an advanced phenomenological model incorporating both the dielectric constant and electrical conductivity in the form of Debye and Cole-Cole representations. Across the frequency range, three distinct relaxation processes were identified: a high-frequency water process and two interfacial processes related to interactions between the aqueous pore solution and mineral particles (membrane relaxation and Maxwell-Wagner effects). Additionally, an apparent direct current conductivity was observed. This comprehensive broadband analysis represents a further step toward the in situ characterization of rocks using electromagnetic field measurement methods and demonstrates advancements in both methodology and understanding of rock properties compared to existing studies.