Complex dielectric properties of organic-rich mudrocks as functions of maturity

Abstract

Complex dielectric variations can address neatly the maturity of organic-rich mudrocks. We, therefore, apply an open hemispherical cavity resonator to measure complex dielectric permitivitties of five thin sections of oil (bakken) shales (with different maturity) of $\sim$ 30 $\mu$m thickness on glass-substrates around 2.15 mm thick in 100 - 165 GHz. The real part of complex dielectric permittivity ($\epsilon_{re}$) are constant but show significant differences in magnitude based on maturity: (1) lowest, $\sim$ 1.9, for immature or early maturation stage, (2) higher than the immature one, $\sim$ 3.0 (also bundled up together), for three oil-matured stages, and (3) highest, $\sim$ 4.9, for late or overmatured stage. The conductivity ($\sigma_{re}$) from imaginary part of the complex dielectric constant ($\epsilon_{im}$) emphasizes two important features of conductivity of oil shales: (1) frequency dispersion, and (2) maturity-dependence. We obtain increases of $\sigma_{re}$ with maturity and frequency.