Sedimentary Facies Distribution within the Duvernay Formation, East Shale Basin, Westerdale Embayment, Alberta, Canada
Creators: Baker, Daniel
Publisher: name: University of Alberta Library
Year: 2023

<p>Abstract:<br>
The Upper Devonian Duvernay Formation is composed of basin-filling sediments ranging from floatstones to organic-rich mudstones. The organic-rich mudstones were subjected to the appropriate burial depth, pressure, and temperatures to constitute an unconventional reservoir target. The major development locations are found within the West and East Shale Basins divided by the Rimbey-Meadowbrook (RM) Leduc reef trend. The West Shale Basin is divided into the Kaybob, Edson, and Willesden Green development areas. The East Shale Basin is divided into the Ghost Pine Embayment and the Westerdale Embayment development areas. This study focuses on the identification, characterization, and distribution of sedimentary facies located within the Westerdale Embayment. The Westerdale Embayment is defined by the Rimbey-Meadowbrook (RM) Leduc reef trend to the west and the Bashaw Leduc reef complex to the east.<br>
Eight facies were identified and interpreted from 10 cores. Facies are subdivided based on bioturbation index (BI), trace fossils, colour, sedimentary structures, lithologic accessories, allochems, and nodular textures. Depositional processes are interpreted to include gravity driven sediment flows, bottom water currents, and suspension settling. Proximity to bioherms is the dominating influence on lithological heterogeneity within the embayment: which is directly related to carbonate rich gravity driven sediment flows sourced from the bioherms. Teichichnus are associated with the sediment-gravity flows and they extend into underlying black mudstone beds. Minor Zoophyscos, and Planolites are also observed. Bioturbation is less common in distal portions of the embayment, along with an increasing proportion of black, organic-rich mudstones.<br>
Facies associations were defined and helped to identify correlatable stratigraphic surfaces within the Duvernay Formation. These surfaces are used to demarcate the lower-, middle-, and upper-Duvernay, with the upper surface representing the Duvernay-Ireton contact. The lower-Duvernay in this study is composed of F2 and F3. Facies 2 and 3 form a facies association that is interpreted as middle slope. The middle- and upper- Duvernay comprises varying amounts of F1 and F4. Facies 1 and 4 form a facies association that is interpreted to be basinal. Within the embayment and proximal to the Bashaw complex, all three Duvernay units are observed. Distal from the complex and towards the embayment opening only the lower and upper-Duvernay can be distinguished.<br>
To understand the relationship between facies composition and petrophysical characteristics, two principal component analyses (PCA) are conducted on two separate well data sets (100/08-20-038-28W4/00 and 100/02-19-039-26W4/00). This analysis used Gamma Ray (GR), Deep Resistivity (RESD), and Bulk Density (RHOB) logs. Manual cut-offs were selected and compared to core facies to establish baseline facies petrophysical expressions. Boolean calculations were used to highlight the vertical depths that matched the cut-off criteria of specific facies to extend core information across the embayment. This method provided additional information to consistently recognize the middle-Duvernay surface, which was otherwise difficult to identify. Using the petrophysical expressions of each facies provides a basis for isopach- and net-to-gross maps. These maps are compared to residual structure maps of the Cooking Lake Formation and development locations located within the embayment. Facies distribution correlate well to paleogeography and industry development.</p>