Reservoir Characterization of the Mid-Cretaceous Dakota Formation, Southern Uinta Basin, Utah, U.S.A

Joshua P. Dark¹, Brian S. Currie¹, and Mary L. McPherson^2
1Geology, Miami University, Oxford, OH
²McPherson Geologic Consulting, Vernal, UT

In the southern Uinta Basin of Utah, fluvial channel sandstones of the Albian-Cenomanian Dakota Formation are economic gas reservoirs. Recovery of gas from this formation has proven challenging due to complex stratigraphic relationships between the Dakota and underlying formations, as well as local variability in reservoir-sandstone thickness, distribution, and quality. In order to evaluate the physical characteristics of potential reservoir sandstones, we constructed six photo-mosaics of individual Dakota Formation fluvial channel complexes, measured 13 vertical sections with accompanying outcrop gamma-ray logs, and recorded >1,100 paleocurrent orientations. Dakota Formation channel deposits consist of upward-fining conglomerates and coarse- to fine-grained sandstones. Paleocurrent orientations indicate an overall NE direction of paleo-flow. The geometry of internal bounding surfaces indicates deposition by laterally/downstream accreting marcroforms and in-channel dunes. Individual channel sandstones are 200-1000 m wide and 8-15 m thick and in places form amalgamated sheet-like bodies that are up to 3 km wide and 40 m thick. Outcrop data were compared with subsurface geophysical/petrophysical and production data from the southern Uinta basin to evaluate possible ties between channel sandstone attributes and hydrocarbon occurrence. Based on these comparisons the primary controls of economic gas accumulation within the Dakota Formation are depth, stratigraphic position, and reservoir architecture. Secondary controls include structure, fracturing, and diagenesis. The lowest risk interval to pursue is the amalgamated sheet sandstones of the basal Dakota Formation.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas