Bakken/Madison petroleum systems in the Canadian Williston Basin. Part 3: geochemical evidence for significant Bakken-derived oils in Madison Group reservoirs

There have been two different definitions of the Upper Devonian- Mississippian Bakken/Madison petroleum systems in the Canadian Williston Basin. Early studies proposed the Bakken shales as the source for oils in both the Bakken Formation and Madison Group reservoirs. More recent studies suggested two separate sources for these oils, thus the Bakken oils were interpreted to be derived from the Bakken Formation shales and the Madison Group oils from a carbonate source within the Madison Group. The present study utilized quantitative results of molecular markers across gasoline-range light hydrocarbons, saturated and aromatic hydrocarbon fractions in 122 oil samples to re-evaluate the oil/oil and oil/source relationships. The steroid and hopanoid parameters collected in this study have confirmed the diagnostic features for end-member Bakken and Lodgepole sources, whereas a range of other molecular markers revealed compositional continuums occurring between the two oil families. The recognition of more extensive mixing of Bakken-derived oils in Madison Group reservoirs along a SW-NE trending fault/fracture zone in southeastern Saskatchewan indicates focused migration pathways for Bakken oils and thus upward resource potentials. The results also suggest caution with the use of conventional biomarker data in oil/oil and oil/source correlation when the different sources concerned contain biomarkers in drastically different concentrations. (C) 2002 Published by Elsevier Science Ltd.