Soil-Gas Evaluation of a Greybull Prospect, Crow Reservation, Montana: A Case Study
Lopez, David A. 1, Daniel H. Vice2 (1) Montana Bureau of Mines and Geology, Billings, MT (2) Penn State University, Pottsville, PA
A regional stratigraphic and oil and gas investigation of the Lower Cretaceous Greybull Sandstone in the region of the Crow Indian Reservation, south-central MT was undertaken in 1996 with funding from the National Technology Laboratory, Department of Energy (NETL). Outcrop and subsurface work revealed five major Greybull channels crossing the Crow Reservation. Three exploration leads were identified where Greybull valley-fill sandstone was potentially in a favorable structural configuration to trap an oil accumulation.
Because well control is limited in the area, a geochemical soilgas exploration program was conducted to help confirm these leads with additional funding from the NETL. The soil-gas survey resulted in excellent anomalies in ethane, propane, and butane + pentane over one of the leads near the town of Crow Agency. Methane data did not show an anomaly. The anomaly in the heavier fractions was interpreted to indicate a heavy-oil source in the subsurface, which is typical of oil accumulations in the Greybull in the surrounding region.
Subsequent to the publication of these results, the Crow Tribe’s oil and gas committee conducted a seismic survey over the Crow Agency lead confirming the presence of the structure as originally mapped and a well-developed Greybull valley-fill sequence. The Tribe was successful in marketing the prospect and as of the end of January, 2006 the first exploration well has been approved and permitted.
AAPG Search and Discovery Article #90055©2006 AAPG Rocky Mountain Section Meeting, Billings, Montana