--> The Wasatch/Mesaverde Petroleum System of the Uinta Basin, Utah and Piceance Basin, Colorado: A Unique Model for Basin-Centered Gas Accumulations, by L. MacMillan and L. C. Gerard; #90986 (1994).

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Abstract: The Wasatch/Mesaverde Petroleum System of the Uinta Basin, Utah and Piceance Basin, Colorado: A Unique Model for Basin-Centered Gas Accumulations

Logan MacMillan, Leo C. Gerard

Gas production in the Uinta and Piceance basins presently encompasses more than 1500 sq mi (3900 sq km). Non-associated gas production from multiple, discontinuous fields can be best described and understood from the perspective of several separate petroleum systems. The most shallow, regional gas reservoirs are the predominantly fluvial sandstones of the Paleocene Wasatch Formation, and the underlying Maastrichtian Mesaverde Group. Four independently-derived relationships demonstrate the Wasatch/Mesaverde as a unique Petroleum System.

When viewed in a regional perspective, the producing areas of both basins demonstrate a significantly different model for a central-basin gas accumulation than those examples previously described in the literature (Basin Dakota of the San Juan basin; Wattenburg "J" Sandstone in the Denver basin, Elmsworth of the Deep Alberta basin.) In the case of the Wasatch/Mesaverde petroleum system of the Uinta and Piceance basins, the gas-prone source rocks have expelled methane from the coals at the coal rank of Medium Volatile Bituminous, and that gas has displaced the free moveable water within the pore-structure over a vertical and stratigraphic thickness of 6500 ft (2170 m).

The four relationships of the Wasatch/Mesaverde Petroleum System are: first: regional lithostratigraphic analysis to differentiate source rocks, reservoir rocks and seals; second, gas analysis of the produced gas in the basins (Rice, 1992); third, the correlation of the thermal maturity pattern of the deep Mesaverde coal deposits (Nuccio and Johnson, 1986, 1983) to wells with the higher Estimated Ultimate Recovery (EUR); and fourth, reservoir characterization and petrophysical modeling (Hartmann and MacMillan, 1992) that indicate characteristics similar to other regional central basin gas accumulations.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994