High-frequency complex permittivity of shales (0.02-1.30 Ghz)

This study describes a new approach to analyze complex permittivity data of shales and to extract fundamental properties relevant to engineering applications. The complex permittivity at high frequencies was measured for three different shales: Queenston, Mancos, and Pierre shales. Plane surfaces parallel and perpendicular to the bedding plane were cut from well-preserved cores. Permittivity data were acquired using a coaxial termination probe and a network analyzer (0.02-1.30 GHz). It is shown that Pierre shale displays high complex permittivity values relative to Queenston nd Mancos shales. A simple approach is adopted to extract the volumetric free-water content of shales based on permittivity data at high frequencies. Shales with high specific surface (e.g., Pierre shale) show the lowest free-water content among tested cores. The slope of the relationship between real permittivity and frequency in a semi-log plot is suggested to relate permittivity data to the specific surface. The anisotropy in complex permittivity is a potential parameter in shale characterization. The permittivity anisotropy depends on the reactivity and the clay content of the shale, as well as on the inherent fabric anisotropy.