Geochemistry and familial association of crude oils from the Birdbear Formation in southeastern Saskatchewan, Williston Basin

The geochemical composition of nine (9) crude oil samples from the Upper De vonian 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 Mi ddle Devonian Winnipegosis pinnacle reefs, can be resolved from a set of tw enty one (21) Winnipegosis-reservoired oils on the basis of a range of geoc hemical parameters. A detailed geochemical oil-oil correlation reveals that these stratigraphically separated groups have variable gasoline range char acteristics, 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 terpan e 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 h igh 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 natu re, 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 Birdb ear-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 mult iple source character of these oils.