ABSTRACT: Greater Natural Buttes Field, Uinta Basin, Utah: An Example of Enhanced Tight Sands Gas Accumulation

John C. Osmond

Gas is produced from tight sands interbedded with carbonaceous shales and coals of the Upper Cretaceous Mesaverde Group in several basins of the Rocky Mountain region. The Greater Natural Buttes area (cumulative production, 290 bcf of gas at 18 bcf of gas per year) is an example of where Mesaverde gas has migrated 2000-4500 ft along faults and accumulated in lenticular fluvial sandstones enclosed in red beds of the Eocene-Paleocene Wasatch Formation. The Wasatch sandstones have better reservoir properties and therefore better economics than those of the Mesaverde.

The northwest trending faults appear to have been active during deposition of the Eocene lower Green River Formation, which overlies the Wasatch. There appears to be a genetic relationship between the faults and the northwest-trending, tensional fractures filled by gilsonite dikes that cut, but do not vertically offset, the Green River and overlying Eocene (and Oligocene ?) beds. Areal distribution of the dikes may correspond with the subsurface distribution of the faults but closely corresponds with the area of Wasatch gas production.

The chemical composition of the gases from the Mesaverde and Wasatch at Greater Natural Buttes are very similar, supporting the concept of a common source in the Mesaverde.

In mature basins where tight sands are not economic, exploration offers near-term returns for tight sands gas that has migrated into more economic reservoirs.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990