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Abstract: A Deep Basin Gas Model for Lower Cretaceous Hydrocarbon Distributions, Powder River Basin, Wyoming


The Lower Cretaceous Muddy and Dakota formations are prolific producers of hydrocarbons in the Powder River Basin, Wyoming. The Muddy Formation has produced over 400 MBOE from shoreline, valley fill, and estuarine sandstones. Similarly, the fluvial sandstones in the Dakota Formation have produced over 100 MBOE. The predominant trap mechanisms for these hydrocarbon accumulations are complex stratigraphic traps, with a few combination structural-stratigraphic traps.

Similar to the Lower Cretaceous Mannville reservoirs in the Alberta Basin, Canada, a regional division between up-dip conventional hydrocarbon reservoirs, and down dip, deep basin type hydrocarbon accumulations can be distinguished. Fields such as Bell Creek, Coyote Creek, Recluse and, Rozet typify the conventional region where normal to overpressured accumulations are surrounded by extensive water bearing reservoirs. Down dip to the west and southwest, Drill Stem Test (DST) data indicate extensive regions of hydrocarbon saturated reservoirs, where hydrocarbons displaced unbound water, up-dip. In these down-dip areas, water free, DST recoveries are reported, delimiting the hydrocarbon saturated regions. Within the hydrocarbon saturated areas, and along the up-dip limit of these saturated regions, porous and permeable reservoirs produce significant quantities of oil and gas. Highlight, Kitty, Amos Draw, and Buck Draw Fields typify the deep basin type of accumulations.

The Lower Cretaceous Muddy and Dakota Formations in the Powder River Basin offer tremendous potential for discovering new hydrocarbon accumulations. While much of the up-dip conventional play has been extensively explored, large, relatively under-explored regions within the deep basin hydrocarbon saturated window may contain large hydrocarbon accumulations.

AAPG Search and Discovery Article #90946©1997 AAPG Rocky Mountain Section Meeting, Denver, Colorado