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 appli cations. The complex permittivity at high frequencies was measured for thre e different shales: Queenston, Mancos, and Pierre shales. Plane surfaces pa rallel and perpendicular to the bedding plane were cut from well-preserved cores. Permittivity data were acquired using a coaxial termination probe an d a network analyzer (0.02-1.30 GHz). It is shown that Pierre shale display s high complex permittivity values relative to Queenston nd Mancos shales. A simple approach is adopted to extract the volumetric free-water content o f shales based on permittivity data at high frequencies. Shales with high s pecific surface (e.g., Pierre shale) show the lowest free-water content amo ng tested cores. The slope of the relationship between real permittivity an d 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 o n the reactivity and the clay content of the shale, as well as on the inher ent fabric anisotropy.