Subsurface correlation and structure of the Mancos Shale, Uinta Basin, Utah

Andrew McCauley, Brendan Horton, Robert Ressetar, and Lauren Birgenheier

The University of Utah and the Utah Geological Survey (UGS) are at the midpoint of a three-year, multidisciplinary study of the Upper Cretaceous Mancos Shale in the Uinta Basin of eastern Utah. The goals of this project are to provide the industry with an assessment of the natural gas potential of the Mancos and to define the most prospective zones within this 4000-foot-thick stratigraphic unit. The data for the subsurface correlation are from more than 150 well records from UGS and Utah Division of Oil, Gas, and Mining files, supplemented with data donated by industry partners. We have tied our correlations to published stratigraphic sections, mostly around the basin perimeter, and extended the correlations through the interior of the basin. From these, we are constructing isopach and structure maps on the main components of the Mancos Shale: the Mancos B/Prairie Canyon Member, the lower Blue Gate Shale, the Juana Lopez Member, the Tununk Shale, and the Coon Spring/Dakota silt. Further log analysis will undoubtedly lead to recognition of subunits within these strata. In addition, the well logs have been correlated to four wells where core analysis defined 11 lithofacies and related chemofacies, reflecting significant, previously unrecognized heterogeneity in the Mancos. Basinwide log correlation will lead to a new chronostratigraphic correlation scheme for the Mancos Shale, and will in turn provide a model for extrapolating data from the other components of this project into areas where data are scarce.

AAPG Search and Discovery Article #90156©2012 AAPG Rocky Mountain Section Meeting, Grand Junction, Colorado, 9-12 September 2012