Mission Canyon (Mississippian) reservoir study, Whitney Canyon‐Carter creek field, Southwestern Wyoming Thrust Belt

Abstract

Whitney Canyon-Carter Creek Field is a giant sour gas and condensate reservoir located in the wyoming thrust belt. Porous dolomites of the Mississippian Mission Canyon Formation contain over 70% of total in place reserves. The Mission Canyon, as observed in conventional cores throughout the field, is a regressive, shallowlng upward sequence which can be divided into seven depositional facies. These facies occur in a lower section of fine grained open marine limestones and dolomites, a middle “main” porosity zone of shallow marine shelf dolomites and interbedded limestones, and an upper interval of mudflat/sabkha dolomites and anhydrites. Most Mission Canyon production occurs from porous dolomites of the middle “main” porosity zone where dolomitized porous mud-rich facies are interbedded with tight lime grainstones or tight, finely crystalline dolomites. Petrographic and carbon-oxygen isotope data indicates two major diagenetic stages. During early diagenesis, mud-rich intervals were dolomitlzed selectively creating sucrosic and moldic porosity. Calcite, anhydrjte, and dolomite cements reduced total porosity during a late diagenetic event. 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. Intercrystalline matrix porosity of 3% or greater is needed for an effective reservoir. 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.