The Bitumen-Bearing McMurray Formation: Description of Reservoir Units in a Large Fluvio-Estuarine Setting from the Athabasca and Christina Rivers Outcrops, Alberta, Canada*
Alain Lejay1 and Catherine Yuill2
Search and Discovery Article #10092 (2005)
Posted September 18, 2005
*Oral presentation at AAPG Annual Convention, Calgary, Alberta, June 19-22, 2005
1Total, Pau, France ([email protected]) (formerly seconded to ConocoPhillips Canada)
2ConocoPhillips Canada, Calgary ([email protected])
The bitumen sands of the McMurray crop out extensively in the Ft. McMurray area and have provided a tremendous opportunity for a detailed study of the facies and geometry of the reservoir units found in subsurface in the vicinity. Photo-panoramas supplemented by detailed sedimentary logs and also by field GR measurements were built. The global architecture of the McMurray Formation is directly influenced by an overall transgressive trend. A basal unit is characterized by fluvio-deltaic facies, including coarse-grained Gilbert deltas. A prominent intermediate unit is characterized by large-scale meandering fluvio-distributary channels that form the known Heterolithic Stratifications. The sedimentary facies, dominated by climbing ripples, show that the tidal activity had a minimal impact on the deposition and suggest that these channels are more fluvial than tidal-dominated. Episodic fluvial flood events are commonly observed and generate numerous occurrences of significant erosion. The last sequences of the McMurray record a marked marine influence with thinner and shalier channels, some being almost entirely bioturbated and interpreted as distributary-lagoonal meandering channels. The sedimentary model from these outcrops can be extrapolated to the surrounding bitumen fields. However, we should be cautious to make comparisons with fields located farther south, as amalgamation and erosion rates are significantly stronger due to a more proximal fluvial setting.
Regional stratigraphic architecture of the McMurray Formation modified after Hein, F.J., Langenberg, C.W., Kidston, C., Berhane, H., Berezniuk, T., and Cotterill, D.K., 2001, A comprehensive field guide for facies characterization of the McMurray Formation, Athabasca Oil Sands, Northeast Alberta: Alberta Geological Survey, Earth Sciences Report 2000-16, 347 p. (also available as a PDF file on CD-ROM).