A Regional Geologic Framework for the Athabasca Oil Sands, Northeastern Alberta, Canada
Frances J. Hein, Brent Fairgrieve, Graham Dolby, 2013. "A Regional Geologic Framework for the Athabasca Oil Sands, Northeastern Alberta, Canada", Heavy-oil and Oil-sand Petroleum Systems in Alberta and Beyond, Frances J. Hein, Dale Leckie, Steve Larter, John R. Suter
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During the past 15 to 20 yr, detailed work conducted by the Alberta government, including the Alberta Geological Survey and the Energy Resources Conservation Board, allows for a better understanding of the Athabasca oil sand deposit, hosted primarily by the McMurray Formation in northeastern Alberta. Much of this work has relied on regional-scale mapping facilitated through lithofacies analysis of outcrops, cores, and well logs, along with petrographic, grain-size, and palynofacies analysis. In the past, the McMurray Formation has been informally subdivided into lower fluvial, middle estuarine, and upper coastal-plain successions. Results from regional lithofacies analysis and stratigraphic correlation and geologic modeling for the Athabasca oil sands show that much of the preserved stratigraphy is fragmented, that no clear distinctions can be made between the middle estuarine and upper coastal plain lithofacies associations, and that no single model applies to the total succession that is preserved. At least five major unconformities and disconformities separate different system tracts, and they should not be considered to be parts of a single entity or single depositional systems tract. Within each of the original systems tracts are preserved remnants of fluvial, estuarine, and bay-fill successions; some of which are amalgamated or juxtaposed to one another, making geologic interpretations and correlations difficult. In areas of reduced accommodation space, not all the paleoenvironments are preserved. This area of reduced accommodation space occurs in the central and southern parts of the Athabasca oil sand area, where most of the existing and future in-situ technologies will be used to produce the bitumen. Recognition of the proper paleoenvironmental setting is critical for the prediction of reservoir heterogeneity, including lateral and vertical segregation of bitumen from overlying gas and water reservoirs that may be thief zones to in-situ (mostly thermal) bitumen production. The development of a regional geologic framework, using the principles of sequence stratigraphy, allows regional mapping within the different time-transgressive systems to be integrated and allows for the full understanding of the geologic framework for the oil sands. This regional geologic framework is being used by the Energy Resources Conservation Board to assess applications for exploration and development of the oil sands and aids in assessing resources and reserves for the province.