Abstract
The Bakken Formation is a prolific oil reservoir within the Williston Basin and has been the focus of extensive horizontal drilling in recent years. The study area encompasses the Viewfield Pool in SE Saskatchewan, host to over 1.3 billion barrels of original oil in place. The stratigraphy and depositional settings of the Bakken Formation in this area are poorly understood, despite a growing body of literature and the relatively high resolution geological dataset. Additionally, the Viewfield Pool serves as an excellent case study for examining a conventional hydrocarbon trap in an unconventional hydrocarbon reservoir.
The Bakken Formation was deposited on a low gradient shallow marine ramp within a shallow epi-continental sea. The Middle Bakken Member consists mainly of bioturbated and dolomitized siltstones, while the Upper and Lower Bakken member consist of organic rich mudstones. A reinterpretation of the sequence stratigraphy shows five distinct systems tracts are represented in the Bakken Formation, and a total of seven unique lithofacies are present. These lithofacies present evidence of a wave dominated shoreline during regressive phases and a tidally influenced shoreline during transgressive phases.
A comprehensive mineralogical model is derived from X-Ray fluorescence, X-Ray diffraction, and point counting. High resolution mineralogical data reveals subtle sedimentary heterogeneity not previously documented, strengthening the sequence stratigraphic interpretation. An inverse correlation is present between porosity and dolomite + calcite content. A positive correlation is present between both porosity and permeability, and quartz content. Detailed reservoir characterization reveals higher rates of hydrocarbon production is associated with increased net pay, low initial water cuts, high quartz content and reduced intensity of calcite cementation.
