Abstract

The Bakken petroleum system of the Williston Basin consists of low porosity and permeability reservoirs in the Bakken, lower Lodgepole, and upper Three Forks; source beds are located in the False Bakken, upper Bakken, and lower Bakken shales. Natural fracturing enhances these low porosity and permeability reservoirs and result in reservoir “sweet spots.” Hydraulic-fracture stimulation and horizontal drilling greatly improves production from the natural sweet spot areas.

Fracturing and fracture swarms are key elements for establishing Bakken “sweet spots.” Fracturing is related to a variety of causes including: 1) regional stress field; 2) local structures created by basement tectonics or salt dissolution; 3) hydrocarbon pore pressure; 4) combinations of the above. The most important type of fracturing appears to be those related to the regional stress field. These fractures are systematic in their orientations (northeast-southwest).

The orientation of horizontal wells in the Bakken petroleum system is critical to maximize recoveries from the Bakken. Most wells are oriented either north-south or northwest-southeast in order to encounter the maximum number of natural fractures.