Integrated Analysis of the Bakken Petroleum System: U.S. Williston Basin

Jack Flannery and Jeff Kraus
Tethys Geoscience, Denver, CO

As much as 300 billion barrels of oil have been generated from Upper Devonian-Lower Mississippian Bakken shales in the U.S. Williston Basin. Recent industry activity has been focused on the middle Bakken siltstone trend in Richland County, Montana. Operators there are enjoying impressive success rates from wells that test 500 barrels of oil per day, on average. Horizontal drilling, completion, and fracturing technology are generally credited with opening up the historically disappointing play. Companies are now extending the play in to other parts of the Basin. Future success will rely largely upon developing a thorough understanding of the play as it is currently being exploited and, especially, upon using that understanding to identify key geologic controls of Bakken prospectivity that can be capitalized on elsewhere.

Regional structure and isopach maps, along with geochemical, thermal, and rock properties data, are used to construct a three-dimensional thermal and fluid flow model of the basin. The model provides unique insight into the evolution of the Bakken petroleum system and allows us to predict reservoir quality, source maturation, and volumes of oil expelled and currently trapped within the middle Bakken. Integration and spatial analysis of modeled results, regional maps, and measured data shed light upon the fundamental geologic variables and relationships that control Bakken prospectivity. Key factors include maximum reservoir temperature, stratigraphic architecture, and small-scale porosity development. We interpret potential for additional middle Bakken exploration down dip from the current siltstone play where the middle Bakken thickens and becomes sandier.