Characterization of Oil Reservoirs in the Lower and Middle Members

of the Green River Formation, Southwest Uinta Basin, Utah

By

Craig D. Morgan, Thomas C. Chidsey, and Kevin P. McClure

Utah Geological Survey, Salt Lake City, UT

S. Robert Bereskin

Tesseract Corporation, Salt Lake City, UT

More than 32 MMBO and 83 BCFG have been produced from carbonate and clastic beds in the lower and middle members of the lacustrine Green River Formation (Eocene), southwest Uinta Basin. The oil-productive beds can be grouped into five reservoirs based on depositional environment, porosity, permeability, lithology, and other producing characteristics. The reservoirs in ascending order are: (1) Uteland Butte, (2) Castle Peak, (3) lower Douglas Creek, (4) upper Douglas Creek, and (5) lower Garden Gulch.

The lower member consists of the Uteland Butte and Castle Peak reservoirs. The Uteland Butte reservoir is a carbonate sequence interbedded with thin shale and sandstone beds. The Castle Peak reservoir produces from channel sandstone beds that are interbedded with limestone and shale.

The middle member is equivalent to the Douglas Creek and Garden Gulch Members of the eastern Uinta Basin. The lower Douglas Creek reservoir consists of thick (100+ feet), but narrow, cut-and-fill sandstone beds. The upper Douglas Creek reservoir consists of amalgamated, lower delta plain, channel sandstone beds. The lower Garden Gulch reservoir consists of isolated individual channel to shallow bar sandstone deposits.

The Uteland Butte is the most widely distributed reservoir, but generally only produces 30 to 60 MBO/well. The Castle Peak reservoir typically has low porosity/permeability and is dependant on fractures for good production. The lower Douglas Creek reservoir has complex internal heterogeneity causing low productivity. The upper Douglas Creek is the most widespread oil-producing reservoir in the southwest Uinta Basin. The lower Garden Gulch reservoir consists of a few isolated beds, resulting in low oil recovery.

AAPG Search and Discovery Article #90004©2002 AAPG Rocky Mountain Section, Laramie, Wyoming