Mission Canyon (Mississippian) Reservoir Study, Whitney Canyon-Carter Creek Field, Southwestern Wyoming Thrust Belt

Jayne L. Sieverding, Patrick E. Flynn, Paul M. Harris

Whitney Canyon-Carter Creek field is a giant sour gas and condensate reservoir located in extreme southwestern Wyoming in the Fossil basin area of the Wyoming thrust belt. Discovered in 1977, the field contains 36 wells within an area 13 mi long and 2 mi wide. Porous dolomites of the Mississippian Mission Canyon formation contain over 70% of total proven reserves.

Hydrocarbons are trapped in a series of complex anticlinal folds which formed on the hanging wall of the Absaroka thrust plate where Paleozoic reservoir rocks were placed in contact with underlying Cretaceous source rocks. The field is divided into the Carter Creek structure to the north and the Whitney Canyon structure to the south.

The Mission Canyon is a regressive, shallowing-upward sequence containing a lower section of fine-grained deep-water open marine limestones and dolomites, a middle "main" porosity zone of shallow marine shelf dolomites and interbedded limestones, and an upper interval of mud-flat/sabkha dolomites and anhydrites.

Most Mission Canyon production occurs from porous dolomites of the middle "main" porosity zone. This section is 300-350 ft thick and consists of porous, dolomitized, mud-rich facies interbedded with tight lime grainstones or tight finely crystalline dolomites.

Reservoir dolomites contain intercrystalline, moldic, and fracture porosity types. The best reservoir intervals have skeletal-moldic and intercrystalline porosity greater than 9% with permeabilities exceeding 0.7 md. Porosity was modified by late diagenetic anhydrite and calcite cementation, possibly related to structural deformation. Reservoir quality is variable between wells.

Porous dolomites are correlatable between wells across the field, indicating horizontal continuity where the section is not interrupted by faults. Interbedded thin, tight limestone layers may restrict vertical permeability.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.