Abstract

The Williston Basin has proven to be a global super basin. Initially, development across this basin was dominated by conventional production from the Madison Group and Ordovician oil systems; however, with the development of unconventional play opportunities, the biggest resource in the Williston Basin is now the Middle Member of the Bakken Formation. The Middle Member was not pursued as a reservoir because of its low porosity and permeability, the low thermal maturity of the juxtaposed Bakken shales, low resistivity, and perceived lack of oil saturation. This paper will review how geochemical data were used to challenge and explain those initial assumptions with particular focus on the discovery and development of the Parshall field. Unconventional and hybrid plays are complex systems, and although much of the geochemical focus details organofacies or maturity concerns, numerous other processes including sorption, alteration, mixing, and evaporative fractionation can and commonly will influence the interpretation of the results and therefore must be considered. The geochemical techniques discussed in this paper are used to calculate oil saturation and more appropriately, mobile oil saturation, from core data requiring accounting for oil evaporative losses to fully define the workings of the Bakken petroleum system and the Middle Member as the key reservoir.

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