Abstract

The fractured Paleocene and Eocene Green River and Wasatch Formations of the Uinta Basin represent viable targets for exploration and development using horizontal drilling techniques. These formations have the following characteristics favorable for horizontal drilling: (1) predictable orientations of natural fractures which, in part, control production, (2) multiple, low permeability reservoirs of sandstone, siltstone, shale/mudstone and limestone, and (3) overpressured zones.

In the Altamont-Bluebell-Cedar Rim fields, for example, the Green River and Wasatch Formations contain an oil-bearing section up to 8,000 ft (2,450 m) thick of which 2,500 ft (750 m) is overpressured. Production is from multiple, generally low matrix porosity, thin-bedded sandstone and siltstone over a thick stratigraphic section. Permeability is often enhanced by vertical fractures with a dominant north-northwest trend. These zones are excellent targets for high-angle slant-hole drilling perpendicular to the fracture trends.

There are four principal fractured reservoirs in the Uinta Basin that could be explored and exploited using horizontal drilling techniques: (1) upper Green River Formation shale and mudstone, (2) lower Green River Formation ostracodal limestone, (3) lower Green River Formation fluvial sandstone, and (4) Wasatch Formation lenticular sandstone and siltstone.

Over 378 million bbls of oil have been produced from conventional vertical wells in the Uinta Basin. Untapped reserves may exist throughout the basin that can be exploited using state-of-the-art horizontal drilling technologies.