River Gas of Utah No. 1 Core: Window Into the Mancos Shale Gas Reservoir

Gustason, Edmund R. "Gus"¹ and Steven Schamel^2
1El Paso Exploration and Production Company, Denver, CO
²GeoX Consulting Inc, Salt Lake City, UT

     Nearly 1700 feet of uppermost Tununk Shale, Ferron Sandstone and Lower Blue Gate Shale members of the Mancos Shale was continuously cored in the River Gas of Utah No. 1 well, located in the Drunkards Wash CBM field (section 36, T14S, R9E). The upper Tununk Shale is dark gray, slightly calcareous, bioturbated, silty claystone with some streaky laminated silty claystone. The lower 200 feet of the Lower Blue Gate is dark gray, bioturbated, silty claystone and streaky laminated silty claystone. The upper 800 feet of the Lower Blue Gate Shale Member is dark gray, calcareous claystone and silty claystone that grades upward into streaky to lenticular bedded silty claystone. Bentonite beds and calcite concretions are common. A few subvertical fractures occur throughout the core but, in general, the core contains few fractures. Abundant trace fossils, including Planolites, Chondrites, Anconichnus, Terebellina, Thalassinoides, and Teichichnus and ammonites and inoceramid bivalves indicate an oxygenated, normal marine shelf environment with abundant organic input. Over 1,000 feet of the Lower Blue Gate Shale has TOC (type II and mixed type II-III kerogen) greater than 1.0%, 680 feet has TOC greater than 1.5%, and nearly 200 feet has TOC greater than 2.0%. Thermal maturity, as estimated from the rank of nearby Ferron coals, is 0.6-0.7% Ro (high-volatile B bituminous). The Lower Blue Gate Shale may be a significant gas reservoir north of the Book Cliffs and beneath the Wasatch Plateau.

AAPG Search and Discovery Article #90071 © 2007 AAPG Rocky Mountain Meeting, Snowbird, Utah