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Basin-Scale Distribution of Pressure, Thermal Maturity, and Other Hydrocarbon-Related Parameters, Wind River Basin, Wyoming

Nelson, Philip H. 1, Joyce E. Kibler2 (1) U.S. Geological Survey, Denver, CO (2) U. S. Geological Survey, Denver, CO

 

In support of an assessment of gas and oil potential in the Wind River Basin, we plotted and mapped properties derived from drill-stem tests (DSTs) including fluid pressures, fluid type, ratios of flowing and shut-in pressures, and formation temperatures. Vitrinite reflectance (Ro), sonic-log indicators of paleo-overpressure, and well-log indicators of the thickness and character of the Paleocene Waltman Shale Member of the Fort Union Formation are also presented.

 

We define moderate overpressure as pressure-depth ratios of 0.5 to 0.6 psi/ft and high overpressure as pressure-depth ratios greater than 0.6 psi/ft. The Madden area is moderately overpressured from the base of the Waltman Shale Member to the top of the Upper Cretaceous Mesaverde Group and highly overpressured below that elevation. The ratio of flowing pressure to shut-in pressure from DSTs, a crude indicator of gas producibility, is high in the Madden area and low in most other areas in the basin. However, a few deep tests in areas lying along the north side of the basin where Tertiary and Cretaceous strata are thickest also demonstrate high overpressure and high ratios of flowing to shut-in pressure.

 

The level of thermal maturity, as indicated by Ro values, generally increases monotonically with depth in wells in the basin interior but exhibits extensive intervals of nearly constant Ro with depth in wells at the basin margin. Consequently, at any given depth, wells in the deep north-central part of the basin have greater Ro values than basin-margin wells. These pressure and thermal maturity data, combined with temperature and well log data, demonstrate the uniqueness of the Madden area in terms of the vertical extent of overpressured gas accumulations, and indicate the potential for similar gas accumulations at depth in other north-central areas in the basin.

 

AAPG Search and Discovery Article #90055©2006 AAPG Rocky Mountain Section Meeting, Billings, Montana