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Stratigraphic Compartmentation of Reservoir Sandstones: Examples from the Muddy Sandstone, Powder River Basin, Wyoming

By
Randi S. Martinsen
Randi S. Martinsen
University of Wyoming Laramie, Wyoming, U.S.A.
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Published:
January 01, 1994

Abstract

The Lower Cretaceous Muddy Sandstone (Viking Formation equivalent) is a thin but complex stratigraphic unit that contains a variety of anomalously pressured compartments. One or more lowstand surfaces of subaerial exposure and erosion (LSEs), numerous transgressive surfaces of submarine erosion (TSEs), and varying lithofacies compartmentalize the Muddy Sandstone stratigraphically on at least three levels. The first level of compartmentation is defined by the relief along the LSE surface(s), which is highly variable and physically divides the Muddy, both vertically and laterally, into older and younger sequences. The second level is defined by the intersection of shales above the TSEs with the LSE (either by onlap or truncation). The third level results from variations in lithofacies. Whereas many of the compartments comprise classic stratigraphic traps consisting of shale (seal) encompassing sandstone (reservoir/compartment), compartments exist wherein sand is juxtaposed against sand without benefit of intervening shales to serve as a seal. In these situations, the seal appears to consist of a paleosol developed beneath the LSE. The distribution and geometries of pressure compartments in the Muddy have a high degree of correspondence to the various scales of stratigraphic compartmentation observed. In all probability, similar levels of stratigraphic complexity characterize many basins. Any analysis of the controls on pressure compartment formation and distribution therefore should incorporate these stratigraphic complexities and not assume that stratigraphic systems are characteristically simple.

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Contents

AAPG Memoir

Basin Compartments and Seals

Peter J. Ortoleva
Peter J. Ortoleva
Department of Chemistry Indiana University Bloomington, Indiana
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American Association of Petroleum Geologists
Volume
61
ISBN electronic:
9781629810935
Publication date:
January 01, 1994

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