Regional and Local Fractures of the Bakken Petroleum System, Williston Basin: Integrating Field Studies and 3-D Seismic Analysis
Stephen J. Angster, J. Frederick Sarg, 2013. "Regional and Local Fractures of the Bakken Petroleum System, Williston Basin: Integrating Field Studies and 3-D Seismic Analysis", Application of Structural Methods to Rocky Mountain Hydrocarbon Exploration and Development, Constance N. Knight, Jerome J. Cuzella, Leland D. Cress
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The consistent low porosity and permeability of reservoirs in the Bakken petroleum system, in the Williston Basin, have increased the need for fracture studies. Although situated in an intracratonic setting, the Williston Basin displays evidence of deformation enabling the presence of regional and local fracturing. In this study, applicable fracture models are utilized to delineate regional and local fracture orientations within the Williston Region. Northwest and northeast regional fracture trends have been determined by integrating results from previous fracture studies, collecting field data at outcrop locations in the Williston Basin Region, and from subsurface three-dimensional (3-D) seismic data in the Williston Basin. A right-lateral wrench fault strain ellipse model is offered to explain these regional trends. Fracture orientations acquired from outcrop sites (Little Rocky Mountains, Big Snowy Mountains, and Beartooth Mountains) also reveal local, structurally controlled, conjugate fracture trends that are parallel or perpendicular to the structural axis. Using curvature analysis on the interpreted 3-D seismic data, local fracture patterns are also observed within the Williston Basin. When regional and local trends are compared, overlap occurs in fracture orientation showing preference to fractures produced from local structures. Regional and local trends are also incorporated into a mechanical stratigraphy study using field observations of outcropping Bakken age equivalent and lithologically similar strata from the Bighorn Basin. Dense fracturing occurs within the middle Bakken equivalent member of the Cottonwood Canyon Formation. Extensive fractures that are perpendicular to bedding are also observed and cut through the lower bounding Three Forks Formation, Cottonwood Canyon Formation, and overlying Lodgepole Formation.
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With increasing industry emphasis on developing “unconventional” tight gas reservoirs and on enhancing recovery from existing fields, geologists are facing diverse challenges in the applications of structural geology. Identifying fracture characteristics within petroleum systems is essential. Understanding the timing of tectonics and the formation of structures is important, as these factors strongly influence hydrocarbon generation, migration, entrapment, and preservation. The purpose in publishing this collection of key papers is to aid future workers in addressing complex interrelationships between structural geology and hydrocarbon exploration and development. The first four chapters of this book focus on structural concepts and techniques. The second part of this book is a collection of Rocky Mountain fault and fracture studies. These well documented studies are valuable reference materials for all petroleum geologists.