Potential Shale Gas Resources in Utah
Michael D. Laine, Thomas C. Chidsey, Jr., and Craig D. Morgan
Utah Geological Survey, Salt Lake City, UT
Shale gas reservoirs in Utah have tremendous untapped potential. These include the Mississippian Manning Canyon Shale, Pennsylvanian Hermosa Group (primarily the Paradox Formation), and Cretaceous Mancos Shale (Prairie Canyon, lower Blue Gate, and Tununk Members) of north-central, southeastern, and northeastern Utah, respectively. Shale beds within these formations are widespread, thick, buried deep enough to generate dry gas, and contain sufficient organic material and fractures to hold significant recoverable gas reserves.
The Manning Canyon Shale is mainly claystone with interbeds of limestone, sandstone, siltstone, and mudstone, and has a maximum thickness of 2000 ft. Total organic carbon (TOC) varies from 1% to greater than 8% with type III (?) kerogen. In north-central Utah, the Manning Canyon was deeply buried by sediments in the Pennsylvanian-Permian-aged Oquirrh basin and is therefore likely very thermally mature.
Cyclic shale units in the Paradox Formation consist of thinly interbedded, black, organic-rich marine shale; dolomitic siltstone; dolomite; and anhydrite. They generally range in thickness between 25 and 50 ft. These units contain TOC as high as 15% with type III and mixed type II-III kerogen, are naturally fractured (usually on the crest of anticlinal closures), and are typically often overpressured.
The Mancos Shale consists of interbedded claystone, siltstone, and very fine grained sandstone. The thickness of potential shale-gas members of the Mancos ranges up to 1500 ft. In the Uinta Basin, vitrinite reflectance at the top of the Mancos ranges from 0.65% to 1.50%; TOC is 1% to 2% with type II to mixed type II-III kerogen.
AAPG Search and Discovery Article #90092©2009 AAPG Rocky Mountain Section, July 9-11, 2008, Denver, Colorado