BERESKIN, S. ROBERT, TerraTek, Inc., Salt Lake City, UT, DAVID E. TAFF, Independent, Salt Lake City, UT, and ROBERT L. BALLOU, Integrated Energy, Salt Lake City, UT

ABSTRACT: Enhanced Fracture Permeability and Unconventional Production Potential Along the Duchesne Fault Zone, Uinta Basin, Utah

The east-west-trending Duchesne fault zone (Duchesne and Uintah counties) is characterized by a segmented series of surface-expressed high-angle faults. These faults are closely associated with complex fracture patterns documented in both the Uinta and Piceance basins. The most obvious fabric orientation is roughly east-west with subordinate patterns occurring in both the northeast and northwest quadrants. Unoriented cores taken near this zone reflect the presence of fractures down through the green shale facies of the Green River Formation (Eocene). Seismic lines also locally support this observation.

In vertical well bores, numerous completion efforts proximal and somewhat distal to the fault zone have resulted in anomalously high production from sandstone reservoirs that commonly possess mediocre log signatures. In these instances, hydraulic fracturing has theoretically accessed the fracture system. In other examples, subtle structural deformation is responsible for enhanced production. Finally, structural closure may be provided by the fault zone itself.

Fracture production clearly exists in the small oil fields south of Duchesne. Other attempts at establishing, look-alike production have been mixed due principally to lack of knowledge regarding completion techniques. Horizontal drilling ventures near the zone probably will produce mixed results because of the stratigraphically variable position of the pools themselves. Water zones also have been encountered near the faults, which locally may mark the southern boundary of overpressurization in this part of the Uinta basin.

AAPG Search and Discovery Article #90993©1993 AAPG Rocky Mountain Section Meeting, Salt Lake City, Utah, September 12-15, 1993.