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Detailed sedimentological and stratigraphic analysis of the Duvernay Formation in the Kaybob area, Alberta, Canada


The Upper Devonian (Frasnian) Duvernay Formation mudstone is a prolific source rock in the Western Canada Sedimentary Basin, believed to have sourced most of the Upper Devonian conventional hydrocarbon reservoirs in Alberta. More recently it has become a significant unconventional reservoir, with development focused on thick, organic-rich, biosiliceous mudstones. A high resolution depositional and sequence stratigraphic model of the Duvernay within the Kaybob area (the most optimal area for prospectivity) will be useful in the identification of the most productive intervals.

The relatively small (roughly 10,625 km2) Kaybob area has roughly 2,000 wells through the Duvernay, approximately 78 of which are cored. Reefs and basinal areas within the study area enable us to analyze facies transitions from proximal to distal areas. Four cores were examined in detail and complimentary extra-thin, thin sections cut for petrographic analysis. Facies were identified based on sedimentary structures, fabrics, trace and body fossils, mineralogy, cement type and abundance, pyrite abundance and form, and abundance and fill of natural fractures. Cores are correlated to petrophysical well logs, and wells are correlated to build a digital regional map of the formation.

Facies include: planar laminated mudstone with local discontinuous pyritized laminae (deposited by hemipelagic suspension settling), planar- and wavy- laminated calcareous silt in mudstone (deposited by turbidity currents or bottom water currents); fossiliferous wackestones (deposited by turbidity currents); bioturbated siliceous, pyritic mudstones (deposited during dysoxic bottom water conditions); and organic-lean nodular limestones (deposited during highstand shedding of reefs). In this order, these facies document a transition from the most basinal to the most shallow water environments.

Three 3rd order cycles, bounded by 4 sequence boundaries, are interpreted to be superimposed on a 2nd order late transgressive systems tract (TST) and early highstand systems tract (HST). These sequence boundaries are located at the base of the Majeau Lake-Duvernay contact, at or near the top of the middle Duvernay member, within the upper Duvernay member, and at the Duvernay-Ireton contact. These stratigraphic surfaces are mapped out to create a digital regional map of the formation and to determine how their character changes across the basin.