The Upper Devonian Grosmont reservoir in Alberta, Canada, is the single largest carbonate bitumen reservoir in the world, with an estimated 400 billion barrels of bitumen in place. The Grosmont bitumen formed from light crude oil via extensive biodegradation, which produced extremely high in-situ viscosities of >1 million cP. Forty nine samples from fifteen wells were selected for rheological behavior, viscosity, and biodegradation pattern analysis. In addition, various methods of viscosity determination were compared. Results indicate that the Grosmont bitumen is essentially a non-Newtonian fluid at in-situ conditions, exhibiting a distinctive shear-thinning behavior at T < 40C. Neglecting this character will cause inaccurate viscosity measurements. The viscosity variations in the Grosmont reservoir are cyclic with depth and are stratigraphically controlled. The bitumen exhibits 3 levels of biodegradation. Biodegradation parameters from hopanes and tricyclic terpanes may potentially be used for bitumen quality prediction.

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The Upper Devonian Grosmont shelf complex is the worlds largest heavy oil deposit hosted in carbonates, with an estimated >50 billion cubic meters (318 to probably 406 bbls) of initial volume in place. At present the Grosmont is not yet under production. This study involves log interpretation, core examination; facies description; strontium, sulphur, carbon, and oxygen isotope analysis. The Grosmont is subdivided into four shallowing-upward cycles. Most Hondo evaporites are part of the Upper Grosmont 3 and Lower Grosmont and were deposited in a series of small, shallow subaqueous brine ponds or in an extensive lagoon. In the eastern part of the area, the Hondo appears to be dissolved resulting in solution-collapse breccias. Other diagenetic processes that were important in shaping the present reservoir characteristics were pervasive dolomitization and dolomite recrystallization, fracturing, and karstification.

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