Unusual crude oils in the Canadian Williston Basin, southeastern Saskatchewan

The Jedburgh well (location: 16-14-27-8W2) was drilled on a small salt dissolution structure in the Williston Basin. The well lies near the Cussed Creek structure, a complex feature involving both Phanerozoic faults that offset the Precambrian basement and the dissolution edge of the Middle Devonian Prairie Formation halite. The chemical compositions of crude oils recovered from cores of Devonian strata in this well are unique in the Williston Basin and unusual in a global perspective, because they contain significant quantities of α-olefins (with the n-C17 alk-1-ene/alkane ratio ranging from 0.28 to 0.72). The gross chemical compositions and distributions of aliphatic biomarkers, aromatic hydrocarbons and pyrrolic nitrogen compounds in the oils indicate that they were generated by high-temperature, short-term pyrolysis of thermally immature organic matter. Their composition indicates that they were not generated in situ, but accumulated in the Jedburgh well after lateral migration from areas that were influenced by post-Devonian magmatic intrusions. The inferred migration distance ( 10 km) suggests that such intrusions occur within the Cussed Creek structure.