--> The Wright Fault Zone, Powder River Basin: An Example of Lineament Control on Hydrocarbon Distribution, by J. R. Forster and J. C. Horne; #90986 (1994).

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Abstract: The Wright Fault Zone, Powder River Basin: An Example of Lineament Control on Hydrocarbon Distribution

John R. Forster, John C. Horne

The Wright Fault Zone is a major southwest-northeast trending linear feature in the Powder River basin. It controls the development of a major paleostructure that influences the migration and quality of hydrocarbons as well as the distribution of lowstand valley-fill reservoirs. A large paleostructural high began to develop along the northern side of this lineament in the Late Permian to early Mesozoic. Recurrent movements throughout the Cretaceous created a series of en echelon, northeast-trending. anticlinal paleostructures over 50 miles long with more than 100 feet of structural closure.

This major paleostructure focused the migration of more than 200 million barrels of oil from hydrocarbon sources into the Minnelusa Formation from Jurassic to Tertiary time. The highest gravity oils (>35% API) in the Minnelusa occur along this paleostructure. Gravities of Minnelusa oil decrease to the north away from the paleo-anticline due to degradation of the oil during remigration caused by Late Cretaceous to Tertiary structuring. The Wright Lineament on the southern side of this paleostructure forms the southern limit of Minnelusa oil production in the Powder River basin.

During the 97.5 Million Year lowstand of sea level, the trend of a major lowstand valley was controlled by the Wright Lineament. Disruption of paleoslope, enhanced fracturing, and dissolution of Permian evaporites by fresh water influx focused the development of a paleovalley along the Wright Lineament during this lowstand. Muddy Sandstone valley-fill deposits accumulated in this valley during the next sea level rise. These deposits form the main reservoirs of the Hilight Field (>100 MMBO reserves).

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994