Laboratory measurements of complex resistivity characteristics of oil shales from Saterdal No.1 corehole, Piceance Creek Basin, Colorado

Laboratory measurements of the complex electrical resistivity characteristics of more than 120 oil shale samples from Saterdal #1 corehole, Piceance Creek Basin, Colorado, indicate the following: (1) The presence of kerogen in wet Green River Formation marls increases their d.c. resistivities from about 300 ohm-m to more than 10⁵ ohm-m, makes them isotropic, and causes a substantial frequency dependence. (2) Microanisotropy coefficient increases with water content from about 2 to as much as 200. The effect seems to be due to an extreme porosity and/or permeability anisotropy, involving a drop in longitudinal resistivity from about 10⁸ ohm-m for dry samples to as low as 10⁵ ohm-m for wet ones, while transverse resistivities stay relatively constant at about 10⁸ ohm-m. (3) Intermediate grade oil shales show the most extreme anisotropy effect; both very rich and very lean oil shales are more nearly isotropic. (4) Both wet and dry oil shales show a pronounced frequency effect for frequencies >10Hz, and may make good IP targets.