Abstract
The Late Devonian Duvernay Formation is a burgeoning shale reservoir within the Western Canada Sedimentary Basin (WCSB) that accumulated as an organic-rich basinal mudrock concurrent with shallow marine carbonates of the Leduc and Grosmont formations. The WCSB is partitioned into the West and East Shale Basins by a narrow, linear Leduc Formation reef complex known as the Rimbey-Meadowbrook trend. Since 2011, Duvernay exploration has been focused in the West Shale Basin. This study characterizes sedimentologic, stratigraphic and geomechanical controls on Duvernay reservoir potential across the East Shale Basin based upon detailed description of core from 42 wells. Ten basinal Duvernay depositional facies were identified, and nine sequence stratigraphic surfaces were correlated across the study area. Geologic attributes were mapped to identify fairways of shale deposition within the East Shale Basin.
Introduction
The Western Canadian Sedimentary Basin (WCSB) of Alberta, Canada is a prolific hydrocarbon province that includes both conventional and unconventional reservoirs (Figure 1). The Upper Devonian Duvernay Shale serves as the source rock for most of the conventional hydrocarbon resources of the WCSB, and more recently (circa 2011) has been successfully targeted as an “unconventional” hydrocarbon reservoir. The Duvernay accumulated as an organically-enriched basinal mudrock during an episode of second-order maximum flooding, and is contemporaneous with shallow marine platform carbonates of the Leduc and Grosmont formations. The WCSB is partitioned into the West and East Shale Basins by the narrow and linear Leduc Formation reef complex known as the Rimbey-Meadowbrook Trend (Potma et al., 2001; Stoakes, 1980; Stoakes and Creaney, 1985). Within both the West and East basins, the Duvernay accumulated in dysoxic marine conditions, and the most organically-enriched Duvernay deposits occur in basinal settings farthest from the equivalent platform carbonates of the Leduc and Grosmont (Chow et al., 1995).
This study defines the sedimentologic and associated sequence stratigraphic controls on Duvernay rock properties and is based upon the detailed description and analysis of 42 continuously cored wells and their associated well logs, and well logs from an additional 216 wells. Four regional stratigraphic cross sections include high quality “modern” well logs and abundant core: two cross sections extend across the West Shale Basin (WSB) and two extend across the East Shale Basin (ESB) (Figure 1). Previous studies of the Duvernay Formation characterize its qualities as a source rock to most conventional reservoirs within the WCSB (Stoakes, 1980; Stoakes and Creaney, 1985; Weissenberger, 1994; Chow et al., 1995; Fowler et al., 2001; Potma et al., 2001; Passey et al., 1990; Passey et al., 2010; Rokosh et al., 2012) and more recently as a prolific shale reservoir within the WSB with development opportunities within the East Shale Basin (Preston et al., 2016; Etam, 2017; Bauman, 2018; Groberman et al., 2018; Currie, 2018; PrairieSky Royalty Ltd., 2019a, 2019b, and 2019c; Wong et al., 2016a; Young, 2019).
