Outcrop and Subsurface Criteria for Differentiation of Sheet and Channel-Fill Strata: Example from the Cretaceous Lewis Shale, Wyoming
E.M. Witton-Barnes, N.F. Hurley, R.M. Slatt, 2000. "Outcrop and Subsurface Criteria for Differentiation of Sheet and Channel-Fill Strata: Example from the Cretaceous Lewis Shale, Wyoming", Deep-Water Reservoirs of the World, Paul Weimer
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The Dad Sandstone Member of the Lewis Shale (Maastrichtian), south central Wyoming, provides a unique opportunity to model the lateral continuity of deep-water turbidite and debrite sandstone reservoirs at an interwell scale in outcrop. Outcrops located within the Sierra Madre Uplift area on the eastern rim of the Washakie Basin have been correlated confidently to subsurface data, allowing rock-based continuity and geometry models generated in outcrop to be carried into and applied in the subsurface.
Outcrop study identified four lithofacies types distinguishable by either specific lithic attributes or geometry. These four lithofacies types include:
Laterally continuous turbidite sheet sandstones exhibiting successions of Bouma Ta to Tb intervals, flat, non-scoured bases with underlying fine-grained deposits, and evidence of rapid dewatering including convolute bedding, dish and vertical dewatering structures.
Laterally discontinuous turbidite and debrite channel-fill sandstones exhibiting characteristics of a high-energy, erosive, confined environment including scour-based beds and an abundance of concentrated rip-up clasts.
Thin turbidite sandstones of variable lateral continuity, interbedded with laminated siltstone and mudstone.
Fine-grained laminated sandstone, mudstone, siltstone, and shale which are proximity indicators to the other three facies types.
An excellent correlation has been established between these deposits in outcrop and STAR™ borehole images of correlative sandstone bodies in the subsurface in the Barrel Springs 7-22 well located 11.2 km (7 mi) west of the outcrop. Qualitative comparison of outcrop and borehole image features, coupled with quantitative analysis of data, including modified Fischer plots, provides diagnostic criteria for characterizing potential sandstone reservoirs intersected in the borehole. These criteria may be used elsewhere to differentiate deep-water facies in outcrop and subsurface data.