Stratigraphy, Sedimentology and Reservoir Characterization of an Inner Platform Carbonate-Evaporite Sequence: the Late Devonian Duperow Formation of Southeastern Saskatchewan, Canada

The Duperow Formation in Southeastern Saskatchewan forms the lower part of Saskatchewan Group. Stratigraphic review of the formation reveals that it consists of three members: Saskatoon, Wymark and Seward, in ascending order. Sedimentological and petrographic analysis of cores and samples from these three members recognizes nine lithofacies: bioclastic wackestone/packstone (Lf1), stromatoporoid floatstone/bafflestone (Lf2), Amphipora floatstone/bafflestone (Lf3), nodular peloidal wackestone/packstone (Lf4), argillaceous dolomudstone (Lf5), dolomitic mudstone (Lf6), microbially laminated dolowackestone (Lf7), anhydrite (Lf8) and halite (Lf9). These nine lithofacies are further grouped into five lithofacies associations (LFA-I to LFA-V) that can be organized into the following five major depositional environments: 1) normal marine subtidal, 2) stromatoporoid bank/mound, 3) restricted inter-tidal mudflat to lagoonal, 4) more restricted intertidal and 5) supratidal.;The major diagenetic processes of the Duperow Formation include micrite envelope and micritization, calcite cementation, dolomitization, compaction, dissolution, anhydrite cementation and fractures. Dolomitization and dissolution are the major factors responsible for the increase of porosity. Calcite cementation and anhydrite cementation contributed to destruction of porosity, and, therefore, reduction of the reservoir quality of the rocks. The stromatoporoid floatstone/bafflestone lithofacies (Lf2) and the microbially laminated dolowackestone lithofacies (Lf1) contain an appreciable amount of porosity resulting in fair reservoir qualities. Visible porosity identified in these two lithofacies varies from about 3% to 10% and consists of vuggy, intercrystalline, moldic and intraparticle porosities. Of these, the intercrystalline and primary intraparticle porosities are the most abundant and common types. The reservoir quality in the Duperow Formation in southeastern Saskatchewan is different from that in North Dakota where it forms the second most prolific oil-producing unit. The degree of dolomitization might be an important reason. In North Dakota, the relationship between the distribution of dolomite porosity and reservoir quality is the result of dolomitization localized adjacent to fracture/fault systems. A similar dolomitization scenario might be attributed to the locally dolomitized zones of southeastern Saskatchewan.