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.