Grosmont Formation Research Articles

Bitumen Accumulation in Grosmont Platform Complex, Upper Devonian, Alberta, Canada

The Upper Devonian Grosmont Formation, a broad carbonate platform complex in Alberta, Canada, contains an estimated 300 billion bbl of bitumen. It has been suggested that these vast reserves are related to Lower Cretaceous Athabasca oil sands. Detailed gas chromatographic-mass spectrometric studies of a wide range of biologic marker compounds confirm this suggestion. The Grosmont Formation contains bitumen of similar maturity and source to the Athabasca deposit, but it has been subjected to a greater degree of biodegradation and water washing, possibly as a result of its reservoir rock characteristics. The difference in the degree of biodegradation is manifested by the absence of bicyclic terpanes and by the reduced concentrations of the C30 and the 22R epimers of the extended hopanes in the Grosmont bitumen. Also, the greater degree of water washing of the Grosmont bitumen is inferred from the observed distribution of the bicyclic, tricyclic, and tetracyclic terpenoid sulfides, which shows a characteristic loss of the lower molecular weight members in the carbonate bitumen. The correlation established here between the two deposits suggests that if the precursor oil has indeed undergone long-distance migration, the Paleozoic carbonates could have acted as a path for migration. Finally, the observed distribution of steranes in the Grosmont bitumen corresponds to the suggestion that the Mannville Group shales were not the major source rocks of the oil-sand and carbonate bitumen accumulations of northern Alberta.

Geological Setting and Production History, Grosmont Pilot Project, Northern Alberta: ABSTRACT

Enormous quantities of bitumen are contained along the eastern margin of the Upper Devonian Grosmont Formation in northern Alberta. This formation can be readily subdivided into four informal stratigraphic units which represent, along with several smaller scale internal depositional cycles, successive stages in the evolution of a hugh carbonate complex: argillaceous slope sequences pass upward to a spectrum of shallow-platform facies and these then are capped by shoreline deposits and horizons of exposure and erosion. Although almost exclusively secondary in nature, the type and distribution of pore fabrics appear to have been at least initially controlled by original depositional facies. In 1975, Union Oil Co. of Canada initiated a single well steam stimulation program to evaluate the potential for recovering bitumen from the upper Grosmont Formation. In 1977, the Alberta Oil Sands Technology and Research Authority (AOSTRA) and Canadian Superior Oil joined the project and further tests (steam stimulation, steam drive, combustion) were undertaken at a new site with Union continuing as operator. The 1980-81 huff and puff stimulation program consisted of one injection/production well and four closely spaced observation wells. Four production cycles have been completed to date, yielding attractively high production rates. An expanded evaluation program is currently under way and will utilize a five-spot scheme of injection/production wells augmented by four or more obse vation wells. End_of_Article - Last_Page 578------------