Bakken Equivalent Undeveloped Major Shale-Oil Play in the U.S.
The Great Basin Mississippian/Devonian Pilot Shale is age equivalent with the Bakken Shale of the Williston Basin. However, some of the highly organic rich and thermally mature Pilot Shale is nearly six times thicker than the Bakken and occurs in lateral extensive and coherent thrust sheets at relatively shallow (7000’) depths.
Measured sections with surface gamma-ray logs) greatly supplement the paucity of wells that have penetrated the Pilot oil source shale. Combining measured section data with well data provides a general map of lateral distribution of this promising oil-shale.
Coupled with conodont analysis palynomorph analyses of the outcrop and well cuttings provides information on age, maturity, depositional environment, kerogen type, and richness of the shales and greatly simplifies the nomenclature. This fossil data indicates that the shales are oil-prone marine, thermally mature and organically rich.
The surface gamma-ray log allows identification of strata with the highest organic content. X-Ray Florescence (XRF) analysis of the hand samples and cuttings provide another tool for correlating surface and subsurface sections and correlation between source shales and oil. For example, oil from the Blackburn field in Pine Valley contains elevated values of vanadium. XRF analyses of Pilot Shale in the adjacent Piñon Range and in the Fish Creek Range on strike to the south also show elevated values of vanadium.
A new Great Basin geological survey, conducted by the authors, constrained with nearly 55,000 precisely located attitudes combined with lithologic descriptions and integration of published geologic maps indicates that the Pilot Shale occurs at relatively shallow depths in extensive, lateral cohesive thrust sheets. Gravity data is used to fill the gaps between outcrop and well data. The authors have greatly improved the existing commercially available gravity by merging it with nearly 20,000 highly accurate, modern proprietary terrain-corrected gravity stations.
The authors are now engaged in creating restorable balanced structural cross sections constrained with the new surface mapping and more than 200 well studies. The structural models are confirmed by comparing the calculated gravity profile with the observed gravity profile.
AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California