Shallow Thermogenic Shale Gas in the Rocky Mountains

Nicholas B. Harris, Department of Geology and Geological Engineering, Colorado School of Mines, 1516 Illinois Street, Golden, CO 80401, phone: 303-273-3854, fax: 303-273-3859, [email protected]

The presence of considerable reserves of thermogenic gas associated with shallow, low maturity shales in the Uinta, Piceance and Green River Basins is indicated by four lines of evidence: mudlogs, gas produced from a Uinta Basin well, gas desorption experiments on GRF core, and gas composition. This is noteworthy in that gas generation is generally considered a process that occurs at high temperatures and thermal maturities. However, studies over the last 20 years suggest that a model of gas generation as an exclusively high temperature process is incomplete. Well-constrained field studies (e.g. Western Canada sedimentary basin, Williston basin) and experimental studies (e.g. Green River Formation (GRF) oil shales in the Piceance Basin) indicate that large volumes of gas are generated in some source rocks at low temperatures and low thermal maturity, at temperatures lower than 62°C and thermal maturities from 0.3% to 0.7% Ro.

Initial studies are underway to document the occurrence and distribution of shallow GRF shale gas in the Uinta Basin, and to relate the distribution to burial depth, thermal maturity, organic carbon content and stratigraphy. Preliminary data suggest that gas content is directly related to %TOC and that gas contents approach values for the prolific Barnett Shale in the Forth Worth Basin, Texas. However, a lack of basic data on this resource, including gas storage mechanisms, the role of natural fractures, logging and seismic techniques for mapping gas, and production technologies, is an obstacle to development of this resource.