A PETROLEUM SYSTEM STUDY OF THE CRATONIC WILLISTON BASIN IN NORTH DAKOTA, U.S.A.: THE ROLE OF THE LARAMIDE OROGENY

The Williston Basin is a Phanerozoic intracratonic basin located in the northern USA (North Dakota, South Dakota and Montana) and southern Canada (Manitoba and Saskatchewan). The basin is known as a major hydrocarbon-producing basin in North America, with a petroleum system characterized by multiple source rocks and reservoirs. The aim of this study is to increase our understanding of the Williston Basin’s petroleum system in the North Dakota region. A detailed analysis of the source rocks in the basin will increase our knowledge about their generation potential and maturity, which could allow the identification of new prospective reservoirs. The source rocks have an average of total organic carbon content between 0.59 and 17.63%, and are type II kerogen, except for the Tyler Formation which is type III kerogen. This gives these formations a good quality status as a source rock, and potentially oil-and-gas prone source. Geochemical data (vitrinite reflectance %Ro, in this case) were used for model calibration. Results show a heat flow range between 41.91-65.14 mW/m2, with higher values toward the center of the basin in North Dakota where the sediment package thickens, and lower values toward the edges. My models predict that the end of the Upper Cretaceous is a critical period in the basin, when peak maturation and hydrocarbon generation are found for every source rock. In this same geologic time an increase in temperature is observed in the North Dakota area, as well as the maximum burial period. Subsidence curves show a slow and long tectonic subsidence period across the basin, with rapid subsidence stages during the Carboniferous in the center of the basin in North Dakota.