Print this pageAlthough the Upper Cretaceous Lewis Shale and Fox Hills Sandstone of south-central Wyoming contain an estimated total resource of 10.7 Tcfg, only 0.6 Tcfg has been exploited because reservoirs are difficult to target and produce. Well-exposed outcrops of these formations along the flanks of the Great Divide and Washakie basins, and a wealth of subsurface data in the basins provide a unique opportunity to study these formations. Outcrop and subsurface correlations suggest the formations were deposited in marginal marine-shelf-slope-basin environments. Outcrop investigations suggest the reservoir sands of the Lewis were deposited as discontinuous and sometimes channelized sands in a deep-water setting (below storm wave base).
The purpose of this study is to better characterize the stratigraphy and reservoir characteristics of the formations by integrating outcrop and subsurface data. The product will be a reproducible sequence stratigraphic-based correlation strategy that can be used to predict sand occurrence, sand geometry, and depositional environments of the formations. This technique may be applied to formations deposited in similar environments elsewhere, most notably deep-water/subsalt Gulf of Mexico.
Methods employed are: 1) Measure, describe, and outcrop gamma-ray log a number of closely spaced stratigraphic sections and interpret a 4th-order sequence stratigraphic framework. 2) Correlate outcrop gamma-ray logs and sequence stratigraphic framework into the subsurface by use of well logs and 2-D seismic data. Local shale markers, well log signatures, core descriptions, and seismic facies will be used to interpret geometries of Lewis sands. 3) TOC data from organic rich shale beds, mappable across the basins, will be used to estimate Lewis Shale source-rock quality.
AAPG Search and Discovery Article #90925©1999 AAPG Foundation Grants-in-Aid