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An Integrated, Core-focused Facies and Stratigraphic Model of the Mancos Shale, Uinta Basin

Robert Ressetar, Lauren Birgenheier, Laini Larsen, Andrew D. McCauley, John McLennan, and Brendan Horton
Utah Geological Survey

A major challenge to successful hydrocarbon production from the Upper Cretaceous Mancos Shale in the Uinta Basin is the identification of prospective horizontal drilling target reservoir facies and production 'sweet spots.' This core-poster presentation will attempt to illustrate relationships between core-defined lithofacies and the data from a range of analytical techniques in order to develop a work plan that explorationists can use to locate and predict target horizons in the 4000-ft thick Mancos. Although in outcrop the Mancos Shale appears fairly homogenous, detailed core descriptions reveal a variety of mineralogic compositions and sedimentary structures and textures that suggest non-uniform geomechanical properties. The core analysis also defines several depositional facies in prodelta, mudbelt, and sediment-starved shelf environments. We have further characterized these facies using thin section, x-ray diffraction, x-ray fluorescence, and QEMSCAN analyses, among others. Results indicate distal sediment-starved shelf deposits have the best combination of hydrocarbon production, storage capacity, geomechanical properties, and reservoir potential. In contrast, the petrophysical data suggest that the proximal mudbelt facies, with its higher water saturations and lower TOC and carbonate contents, is less prospective for hydrocarbon production. Log-based sequence stratigraphic correlations indicate that the distal sediment-starved shelf deposits formed in late transgressive and early highstand sequence sets, whereas the proximal mudbelt facies represent late highstand and lowstand sequence set deposition. These results point towards a methodology whereby explorationists can rank potential Mancos targets for drilling, stimulation, and completion.

AAPG Search and Discovery Article #90169©2013 AAPG Rocky Mountain Section 62nd Annual Meeting, Salt Lake City, Utah, September 22-24, 2013