ABSTRACT

The tectonic setting of horizontal production from the Bakken Formation (Devonian/Mississippian) in southwestern North Dakota is clearly described in terms of lineament block tectonics. Zones of weakness in the Precambrian basement have periodically reactivated to influence development of fractured reservoirs and generate surface expression of structural blocks. Lineament zones interpreted from Landsat linear features and from subsurface structure maps outline a major lithosphere block in the southwestern Williston Basin. The Bakken fairway lies within this regional block.

The regional block is subdivided into a series of smaller constituent blocks, including a triangular structural terrace along the southwest side of the large block. Major production within the Bakken fairway is mainly in the central portion and northern margin of the triangular terrace. There are two separate structural domains along the north terrace margin: in the west, small structures trend oblique to the margin, and in the east, small north-south structures terminate at the margin. In the central terrace the regional structural gradient is low and local structures trend north-south. These three separate tectonic settings each have different Bakken production statistics. The western segment of the northern terrace margin has a low ratio of horizontal to vertical initial production (IP) and a low estimated ultimate recovery (EUR); the eastern terrace margin has a high IP ratio and high EUR; and the central terrace has intermediate values for the IP ratio and EUR. Different production histories probably are the result of heterogeneity differences in fractured reservoirs in each of the three distinct structural settings.