Petrofacies Characterization of Bakken Shale in the Williston Basin, North Dakota
Bakken petroleum system (Late Devonian- Early Mississippian) in the Williston basin of North Dakota and Montana is one of the largest unconventional oil plays in North America with an estimated 7.4 billion barrels of undiscovered oil reserve (United States Geological Survey, 2013). Although Bakken along with Three Forks formations have underwent horizontal drilling and hydraulic stimulation throughout the basin, several uncertainties remain including facies variation due to depositional and diagenetic controls on mineral composition and organic matter content in the shale members, which play a significant role in hydrocarbon production. Characterization of Bakken shale petrofacies is important to better understand depositional environment, facies distribution and their influence on hydrocarbon production. Bakken Formation consists of two world class source rocks (Upper Bakken and Lower Bakken shale) that sandwich the Middle Bakken. Middle Bakken is composed of mixed lithologies including sandstone, dolomite and carbonate. Upper and lower shale members are considered to have been deposited under relatively deep marine anoxic conditions (>200 meters depth), whereas Middle Bakken has been deposited in an epicontinental sea under shallow-water high-energy conditions (< 10 meters depth). The study uses logs, cores, XRD and rock-eval pyrolysis data to investigate petrophysical characteristics of the Bakken Formation. Core parameters were calibrated with log characteristics as well as a series of mineralogy and lithology cross-plot solutions were obtained to define different petrofacies units in shale members resulting in isopach maps of respective facies units to visualize vertical and areal extent of the Bakken shale lithofacies. The study shows that mineralogy, kerogen type and thickness of different shale units contribute much to the oil production.
AAPG Datapages/Search and Discovery Article #90189 © 2014 AAPG Annual Convention and Exhibition, Houston, Texas, USA, April 6–9, 2014