There are two opposing schools of thought that infer either the Bakken Formation or the Lodgepole Formation as the primary source rock for the Madison-reservoired oils in the Canadian Williston Basin. A recent geochemical study revealed evidence indicating the existence of significant mixing of Bakken and Lodgepole oils in the Madison reservoirs. To investigate the geographic distribution of the oil compositions, we employed a multivariate statistical method to extract source and maturity-specific geochemical signatures from a geochemical data set for spatial analysis. Oil mixing appears to be geographically dependent and restricted by a northeast-southwest–striking zone (Torquay-Rocanville trend) in southeast Saskatchewan. Thus, fracture or fault systems are inferred to have provided high-permeability zones allowing Bakken-derived oil to migrate upward across the Lodgepole Formation. The areas without significant fault or fracture systems favor lateral oil migration along porous beds, restricting Bakken-derived oil accumulation to pools in Bakken reservoirs and Lodgepole-derived oils to occur primarily in overlying reservoir beds of the Madison Group.

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