Abstract

The geochemical composition of nine (9) crude oil samples from the Upper Devonian Birdbear Formation of southeastern Saskatchewan was determined using GC and GC-MS techniques. The Birdbear-reservoired oils, formerly included within oil Family D of Osadetz et al. (1992) together with oils from the Middle Devonian Winnipegosis pinnacle reefs, can be resolved from a set of twenty one (21) Winnipegosis-reservoired oils on the basis of a range of geochemical parameters. A detailed geochemical oil-oil correlation reveals that these stratigraphically separated groups have variable gasoline range characteristics, especially different Paraffin Indices and distribution of C 7 alkanes ("Mango" parameters), as well as different C 13 -C 30 normal alkane profiles, Pr/Ph, Pr/nC 17 and Ph/nC 18 ratios. The distribution of terpane biomarkers is similar in both groups, although Winnipegosis samples have more pronounced C 34 hopane prominence and Ts/Tm ratios often greater than 1.0. In contrast, sterane biomarker signatures are quite different with a high concentration of diasteranes and prominent C 21 regular steranes in the Birdbear oil samples, and a different relative abundance of C 27 :C 28 :C 29 regular steranes. Such compositional differences are often genetic in nature, suggesting a different source rock for oils found in Birdbear Formation and a separate petroleum system operating in the Saskatchewan Group across Canadian Williston Basin. However, as the geochemical composition of Birdbear-reservoired oils is quite unique, it is also possible that it may have resulted from mixing of Winnipegosis-like oils with hydrocarbons from other sources during a cross-stratal secondary oil migration, demonstrating multiple source character of these oils.

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