Bathymetrically controlled carbonate microfacies of an Upper Devonian (Frasnian) ramp and relationship to correlative reservoirs, western Alberta and northern British Columbia

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Upper Devonian limestones, dolomites and shales of the Western Canada Sedimentary Basin, deposited some 375-380 million years ago, still host huge quantities of conventional and unconventional oil and gas resources. The basin was once a vast complex of shallow-water carbonate platforms and adjacent basins somewhat akin to the present-day Bahamas. The ocean lay to the northwest and west. Many subsurface reservoirs have been studied and compared to outcrop analogues in the Rocky Mountains which provide a three-dimensional view. Platform interiors consisted of shallow lagoons and tidal flats, while carbonate sand shoals and organic reefs formed along platform margins. Sediment was washed off the interiors and onto the adjacent slopes. Carbonate mud, clay, silt and enormous amounts of organic carbon accumulated in the deeper areas, subsequently becoming the hydrocarbon source rocks. One setting that has escaped detailed scrutiny is the ocean-facing ramp that developed when the topographic relief of the platforms decreased. Such rocks are fossiliferous limestones and shales. In one locality in the Willmore Wilderness Park, these strata, belonging to the Mount Hawk Formation, host spectacular reefs that once towered 25 m above the surrounding seafloor. This locality offers a unique opportunity to compare the components in the reefs versus the adjacent and overlying beds. The dataset consisting of fossil composition will enable determination of the evolving water depths on the ramp. This information will be applied to understand the role of bathymetry and sea level changes on subsurface carbonate platform margin architecture and accumulation in adjacent basins. Husky Energy Inc. is currently exploring and developing both conventional and unconventional resources, particularly shale gas, in correlative strata, and the outcrop dataset will provide a better understanding of the stratigraphic evolution, water-column productivity and reservoir development especially around these platforms. This dataset puts Husky at a competitive advantage and will guide planned exploration activities and drilling locations.