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

TL;DR

This study measures the complex dielectric properties of organic-rich mudrocks at GHz frequencies, revealing how dielectric permittivity and conductivity vary with maturity, providing a potential method for assessing shale maturity.

Contribution

It introduces an open hemispherical cavity resonator technique to quantify dielectric properties of shale samples across maturity stages, highlighting their dependence on maturity and frequency.

Findings

Dielectric permittivity increases with maturity.

Conductivity shows frequency dispersion and maturity dependence.

Permittivity remains constant across frequencies for each maturity stage.

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.