Geochemical analysis and familial association of Red River and Winnipeg reservoired oils of the Williston Basin, Canada

Abstract

Light oils reservoired in the Lower Ordovician Winnipeg Formation, Williston Basin, have a unique geochemical signature separating them from previously recognized oil families, most importantly they are geochemically distinct from the stratigraphically adjacent Upper Ordovician Red River Formation oils. Winnipeg oils are characterized in the gasoline fraction by very high paraffin indices (4–16) and variations in C7 parameters. The saturate fraction is distinguished by a high abundance of C20+ n-alkanes, low carbon preference index and low amounts of pristane and phytane. Sterane biomarkers show a predominance of C27>C28≈C29 suggesting an algal source different from that contributing to Red River oils. In addition, the terpane biomarkers of Winnipeg oils show a high abundance of rearranged hopanes including an unknown C30 compound labelled UC30 and 17α (H) C30-diahopanes (C*30), Moreover, these oils have unambiguous amounts of 18α (H)-30-norneohopanes (C29Ts) which are in low abundance in Red River Formation oils. Geochemical analysis of Lower Ordovician Winnipeg Formation reservoired oils from the Williston Basin suggests that an additional hydrocarbon source, not yet defined, may exist.