WBPC2019 Abstract #5:
The Viewfield Bakken field in SE Saskatchewan is positioned on the northern flank of the Williston Basin and the field covers an area of approximately 877 square miles and has 4 billion barrels OOIP. In the basin center active oil generation in the Upper and Lower Bakken shales has formed an unconventional continuous hydrocarbon system in the Middle Bakken sandstone however the Viewfield area has never been in the oil generation window and represents a conventional accumulation where oil migrated and was trapped in the Viewfield area.
Conventional oil pools share the concept of secondary hydrocarbon migration and entrapment where hydrocarbons accumulate in either structural traps that have 4-way closure or stratigraphic traps where porous reservoir beds terminate into seals. The Viewfield Bakken field does not entirely fit into either classic model but instead the accumulation is largely trapped by a pressure displacement barrier.
The pressure displacement barrier is controlled by the balance of oil density, water salinity, pore throat size and the height above free water. These variables can constructively interfere to raise oil saturations and cause hydrocarbon accumulation within the field or destructively interfere to prevent the displacement of formation water along the periphery of the field and thus create the mechanism for entrapment.