Natural Fractures and Strain Accommodation in the Tensleep Formation at Beer Mug Anticline
Scott P. Cooper, 2013. "Natural Fractures and Strain Accommodation in the Tensleep Formation at Beer Mug Anticline", 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 Pennsylvanian-age Tensleep Formation in south-central Wyoming is comprised of repeated limestones, sandy limestones, and sandstones. Strata of these varied lithologic units are folded over Beer Mug Anticline and cut by numerous intersecting fractures. The anticline, with a near-vertical forelimb and backlimb dip up to 50 degrees, provides an ideal analog for fracture systems in tightly folded Paleozoic hydrocarbon reservoirs. Fracture type and degree of development vary systematically with lithology, structural position, and degree of folding. Fracturing is most intense towards the core of the anticline, which locally consists of folding. Fracturing is most intense towards the core of the anticline, which locally consists of brecciated, oil-stained rock with large-scale vuggy porosity. Most of these strata exhibit inherited (F0) fracture patterns that predate folding, as well as fold-related extension fractures that trend approximately normal (F1) and parallel (F2) to the axis of folding.
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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.