ABSTRACT: Progress Identifying Oil Families and Effective Sources in Williston Basin
K. G. Osadetz, L. R. Snowdon, P. W. Brooks, M. E. Rygh
Analysis of whole oil and saturate fraction compositions from Williston basin oil fields forms the basis for a reevaluation of oil families and effective sources in Williston basin. Gasoline range compositions originally considered important in distinguishing oil families are now considered of limited value. Detailed study of oils and solvent extracts from Canadian Williston basin indicates the nC15+ compositional fraction can be used to effectively associate oils into families and correlate families to their effective source rocks. Ratios of saturate/ aromatic hydrocarbons, pristane/phytane, diasterane/regular steranes, and C23/C30 terpanes provide the most effective criteria for distinguishing four compositionally distinctive il families of restricted stratigraphic distribution. One family is identical to Ordovician sourced oils previously identified. One new family in Middle Devonian rocks is indigenously sourced. The remaining pools are subdivided into two families. The predominant family is sourced from carbonates in the Mississippian Madison Group while the other is sourced from the Devonian-Mississippian Bakken Formation. The Bakken Formation was previously considered the source of both families. Source rocks in both the Bakken Formation and Madison Group are of comparable richness and separated by a thin stratigraphic interval ensuring comparable thermal histories. The apparent effectiveness of Madison sources compared to the Bakken sources remains an unsolved problem. The family classification can be e tended into the American Williston basin using a select sample set and compositions reported in the literature. Other oils distinctive in composition to the families recognized in Canada are present in the United States. The sources of many of these oils remain to be identified.
AAPG Search and Discovery Article #91002©1990 AAPG Rocky Mountain Section Meeting, Denver, Colorado, September 16-19, 1990