--> --> Sedimentological Controls on the Resource Potential of the Devonian Winnipegosis and Duperow Formations in Manitoba

Eastern Section Meeting

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Sedimentological Controls on the Resource Potential of the Devonian Winnipegosis and Duperow Formations in Manitoba

Abstract

Along the eastern margin of the Williston Basin, there is still considerable potential for new plays as only limited deep-well information is available. Oil shows have been documented in almost all Devonian formations but no economic discoveries have been made in these formations to date. We have investigated the sedimentology and organic petrology of the Middle Devonian Winnipegosis Formation and the Upper Devonian Duperow Formation in Manitoba with the goal of understanding the sedimentological controls on their reservoir and source rock potential. Detailed core examination, carbonate and organic petrography, geochemistry and Rock-Eval pyrolysis were done for this project. The Winnipegosis Formation in Manitoba consists of fossiliferous dolostones and limestones, up to ∼100 m thick, which are divided into a lower member of ramp facies and an upper member of rimmed shelf-to-basin facies with isolated reefs. Potential exists for conventional reef and platform plays in dolomitized facies which have up to 35% intercrystalline and vuggy porosity. Bituminous laminites in ramp and platform strata are up to 70 cm thick and have total organic carbon values of up to 52%, suggesting potential for local sourcing. These bituminous laminites are interpreted to be the product of elevated phytoplankton productivity and are best developed in stratigraphic intervals associated with ramp-to-platform/basin and open-to-restricted basin transitions. The Duperow Formation in Manitoba is a 122–195 m-thick succession of limestones, dolostones and evaporites interpreted to represent deposition in the arid interior of a rimmed shelf. The Wymark Member is recognized as the main reservoir unit in the Duperow Formation. Reservoir intervals of porous subtidal and intertidal facies, up to 14 m thick, are capped by tight evaporite facies, up to 3.5 m thick. Facies-controlled dolomitization appears to be the primary control on porosity development, with dissolution as a secondary influence. Massive dolostone and dolomitic microbial bindstone have up to 25% intercrystalline and vuggy porosity and up to 210 mD permeability. Porosity reduction is due to synsedimentary marine calcite cements and burial calcite, anhydrite and gypsum cements. In conclusion, the sedimentology and organic petrology of the Winnipegosis and Duperow formations along the eastern margin of the Williston Basin reveal potential for new conventional and unconventional resource plays.