A reservoir characterization of selected Ordovician, Devonian and Mississippian dolostones from the southeast Saskatchewan portion of the Williston Basin

Paleozoic dolomicrites from the Ordovician to Mississippian have produced oil from various localities in the Williston Basin. Porosity and permeability are two of the most important factors contributing to the reservoir potential of these rocks. Development of porosity and permeability is influenced by depositional environment, stratigraphic distribution and diagenetic history.; The precursors of the dolomites examined were all lime mud-rich rocks with varying proportions of allochems, which suggests deposition below fair weather wave base or in shallow protected settings. Although all of the dolomicrites examined had planar-e to planar-s crystals, there is a distinct crystal size variation between Ordovician-Devonian rocks (30--45 micrometers) and those of Mississippian age (4--15 micrometers). The Devonian Birdbear dolomites from Flat Lake also lie in the latter range.; Crystal size and isotope geochemistry suggest that Ordovician and Devonian dolomicrites have undergone a greater degree of burial alteration than the Mississippian dolostones.; The best reservoir rocks have the following characteristics: planar-e to planar-s crystal form, good intercrystalline porosity, uniformity of crystal and pore throat sizes, good pore throat connectivity, little crystal intergrowth and little to no carbonate or evaporite plugging interstices.; It is recommended that future work on dolostone reservoir characterization should include petrography, geochemistry and geologic mapping to delineate the migration pathways of dolomitizing fluids. A library of MICP data and SEM and thin section photos would help to qualitatively and visually compare productive dolostone to dolomicrite that shows the potential to act as reservoir rock. This thesis can be used as a template for such a characterization.