Petroleum Potential of the Middle Member, Bakken Formation, Williston Basin

Abstract

ABSTRACT The Bakken Formation is a widespread clastic unit between the Mississippian Madison Group and the Upper Devonian Big Valley, Torquay, or Three Forks formations. The formation typically consists of three members: a lower and upper organic-rich shale and a middle calcareous sandstone and siltstone. The three members of the Bakken Formation exhibit an onlapping relationship, and converge and thin toward the margins or marginal shelf areas of the Williston Basin. In Manitoba, the lower member is absent, except for Waskada field. Several correlative lithofacies have been recognized in the middle member. The lowermost unit of the middle member is a regressive deposit. The upper portions of the middle member show transgressive and regressive cycles, and intertidal deposits interfinger with their distal equivalents. Conventional Bakken production is restricted to areas where it is a thermally mature source rock. The greater part of Bakken production in recent years has been taken from the shale of the upper and lower members, although there are outlying fields which produce from a sandstone within the middle member. This suggests that there has been a migration of Bakken oil from the central portion of the basin. The sandstone unit may provide a conduit for migration.