ABSTRACT

Three compositionally distinct families of oils are recognizable from 34 samples produced from a representative suite of pools in southeastern Saskatchewan. The families are characterized by gross geochemical and C15+ saturate hydrocarbon fraction compositions, obtained by gas chromatography and mass spectrometry-gas chromatography.

Family A (2 pools) oils are characterized by low pristane/ nC17 and phytane/nC18 ratios, high diasterane/regular sterane ratios and low C23/C30 terpane ratios. This family of oils is restricted to Ordovician pools. It is identical to the oils from Ordovician reservoirs in the American portion of the Williston Basin. Family B oils (9 pools) are characterized by cross-plots of the ratio of diasteranes/ regular steranes against either the ratio of saturate/aromatic hydrocarbons or the ratio of pristane/ phytane. Within Family B a group of oils (4 pools) with low C23/ C30 terpane ratios may represent a mixture of oils from families B and A. Family B oils are restricted to pools in the Birdbear Formation, the Bakken Formation and the Madison Group. The most abundant family of oils, Family C (22 pools), is identified by the same criteria used to characterize Family B oils, although they have low diasterane/ regular sterane ratios and low pristane/phytane ratios in comparison to Family B. Family C occurs in the Madison Group and younger reservoirs. A distinctive sub-group of oils in Family C has high saturate/aromatic hydrocarbon ratios. One oil with an intermediate diasterane/ regular sterane ratio may represent a mix of oils from families B and C.

Oils in Families B and C have been previously included in a single family of oils attributed to a Bakken source rock. However, the stratigraphic distribution and compositional characteristics of Family C oils preclude such a derivation. The Madison Group is a more likely source. The Bakken Formation remains a potential source for Family B. Family A is probably derived from an Ordovician source rock.

Other families of oils recognized in the American portion of the Williston Basin are not recognized in southeastern Saskatchewan.