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Stratigraphically trapped petroleum deposits occurring in the Muddy Formation of Campbell County, Wyoming, were studied by using discriminant function analysis followed by Bayesian classification analysis. The data used in this study were obtained from over 600 productive and nonproductive wells in a 720-sq mi area.
A total of 15 quantitative measures (variables) of lithology, porosity, and salinity were computed from the S.P., gamma ray, and density logs from each well. Discriminant and Bayesian classification analyses were used to compute discriminant and probability maps. Discriminant-scores maps were made by two methods: (1) using the total data set of both productive and nonproductive wells, and (2) using only the nonproductive wells. The second type of map more closely simulates the exploration situation.
A map showing probability of oil occurrence was constructed by first partitioning the study area into 64 cells of 9 sq mi each, and then establishing a control area and a test area. In the control area the cells were divided into productive and nonproductive subsets; a discriminant function then was computed. The discriminant function derived from the control area was used as the input for a Bayesian classification procedure to compute probabilities of petroleum occurrence in the test area. The predictions made by the statistical analyses are compared to the actual production in the test area.
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