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The Powder River Basin

January 01, 1994


Low-permeability seals associated with abnormal pressures are most commonly identified by examining vertical pressure profiles and noting the depths at which a major change in the pressure gradient occurs. Alternatively, zones of very low permeability that may act as fluid seals may be identified on the basis of core analyses and well tests. Often, however, there are an insufficient number of direct pressure or permeability measurements to adequately identify the depth and lateral extent of these seals. A method has been developed for estimating porosity and permeability through the use of wireline logs. Multivariate statistical techniques are used to segment the logs and group the segments into electrofacies types. Application of this technique to 18 wells within the St. Peter Sandstone of the Michigan basin shows that the electrofacies characterization reflects both the hydraulic and diagenetic characteristics of the formation. Six electrofacies types have been identified, one of which has characteristics similar to those found within seals in other basins.

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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
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Publication date:
January 01, 1994




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