ABSTRACT

The Mississippian Mission Canyon Formation is a prolific oil reservoir in the Williston Basin. The uppermost member of the formation, the MC-3 unit, is productive in the Pierson field in southwestern Manitoba. In the Pierson area, the MC-3 rocks are characterized by four distinct lithofacies: a) algal laminite/stromatolite facies; b) bioclastic grainstone facies; c) peloidal grainstone facies; and d) vadolite facies. Early diagenesis of the unit consisted mainly of biological micritization and burrowing, marine and freshwater calcite cementation, and dolomitization. Later diagenesis was dominated by dolomitization, anhydritization, compaction and pressure solution, and leaching. Porosity development in the MC-3 member in the Pierson field, like many other Mission Canyon reservoirs elsewhere in the Williston Basin, represents a complex interplay of late-stage fabric-selective dissolution processes coupled with development of intercrystalline porosity and preservation of primary intergranular porosity and diagenetic features.