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3-D Geologic Model of the Lewis Shale in the Great Divide and Washakie Basins, Wyoming

D. Suryanto
Colorado School of Mines, Dept. of Geology and Geological Engineering, Golden, CO

The study is a subsurface interpretation of well logs of the Lewis Shale in the Great Divide and Washakie basins,Wyoming. The intent is to increase the understanding of the petroleum system in the study area. The Lewis Shale consists of deepwater sands deposited in lobes that generally prograded to the south.

Subsurface interpretation involves a petrophysical and stratigraphic analysis utilizing well logs and core data. Previous work has generated a basin-scale stratigraphic model. My project will generate a 3-D geologic model from more than 250 wells.

Certain beds within the Lewis Shale contribute to the petroleum system. The Asquith marker, which contains TOC of 0.5 to 21%, is interpreted to be a good source rock and is thermally mature. The Dad Sandstone member, comprised of channel and sheet sandstones, is interpreted to be a good reservoir. The seal consists of interbedded shales and the upper member of the Lewis Shale. Migration of hydrocarbons most likely occurred along sandstone layers. Sandstone bodies that pinch out against paleostructure or were deposited within shale layers may create stratigraphic traps.

In summary, the construction of a 3-D geologic model will help determine sandstone volumetrics for individual sand lobes. The 3-D model, combined with a map of the top of overpressure and source rock quality, will help develop natural gas resources in the Lewis Shale.

AAPG Search and Discovery Article #90902©2001 AAPG Foundation Grants-in-Aid