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Almond Reservoir Stratigraphy and Its Impact on Well Density Rule Changes in the Greater Wamsutter Development Area

Virginia L. Riggert1, James A. Hornbeck1, David S. Muller1, Brian W. Horn1, G. Earl Norris1, Debra H. Phillips1, Evy Glørstad-Clark1, and James L. Coleman, Jr2. (1) BP America Inc, P.O. Box 3092, Houston, TX 77253-3092, phone: 281-366-5855, fax: 281-366-7671, [email protected], (2) Eastern Region, Office of Regional Geology, U. S. Geological Survey, 12201 Sunrise Valley Dr, Reston, VA 20192

The Greater Wamsutter Development Area (GWDA) includes the Red Desert and Washakie Basins within the Greater Green River Basin, southwest Wyoming. GWDA tight gas fields have produced 2 TCF since the 1970's, mainly from the Late Cretaceous Almond Formation. Initial development was on 640-acre spacing, one well per governmental section. Additional increased density wells were drilled in measured stages, typical of gas developments in the continental United States. By 2002, a limited number of 80-acre density wells were being approved by the Wyoming Oil and Gas Conservation Commission. Concurrently, a number 80-acre pilot wells were being drilled within various Federal Exploratory Units.

From many perspectives it made sense to address 80-acre infill development on a more systematic basis, given the GWDA's the existing level of development and the immense area of 2500 square miles. In 2003, BP initiated a consortium with the five GWDA operators then actively pursuing 80-acre development, to collectively pursue the rule change. Reservoir stratigraphy of the Almond provided the foundation for these regulatory changes. Specifically, the cases for higher well density was made on the basis of significant variability of both thickness and lateral continuity of reservoirs in the Upper, Middle, and Lower Almond coastal plain, shoreline, and tidal sandstones. This was then compared to a modern-day analog. Historical production data was shown to be consistent with such a stratigraphic interpretation. Regulatory changes required to accommodate 80-acre development with flexible well placement were approved in 2004 and 2005.