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Department of Geosciences, The University of Tulsa, Tulsa, OK

Abstract: Fracture Architecture of the Tensleep Sandstone, Bighorn Basin, Wyoming: Surface Analogs for Subsurface Reservoirs

Detailed fracture studies conducted on two reservoir analogs exposed on the eastern of the Bighorn Basin provide insight into the variation of fracture density, aperture, and connectivity in the Tensleep Sandstone as a function of hinge curvature and facies architecture. Study sites include Zeisman Dome, an asymmetric, curvilinear doubly plunging dome and Brokenback Anticline, an asymmetric, straight hinge anticline. Both features are interpreted as fault propagation folds.

Tensleep C and D parasequences in Zeisman Dome are cut by fracture clusters that are proportionally spaced according to curvature of the domes hinge. Fracture density within the clusters is significantly higher than the surrounding host rock. Some clusters show evidence of right lateral slip related to the emplacement of the dome. Most of the fracture clusters show both vertical and lateral continuity and connectivity. Fracture characteristics and density change with lithology. Fracture density is intermediate in the dune facies and fractures show significant shear banding. Fracture density is greatest in marine units and fractures are open and well connected. Fracture density is lowest in interdunes and fractures are largely closed. Fractures clusters are not found in Brokenback Anticline, but fracture density is facies dependent.

Work to date indicates that the interplay between fracture and facies architecture in the Tensleep Sandstone will have significant effect on reservoir compartmentalization.

AAPG Search and Discovery Article #90919©1999 AAPG Rocky Mountain Section Meeting, Bozeman, Montana