--> --> From Williston to the edge of the continental plate - a Rockies contrast in Mississippian-Devonian resource basin aspect ratio and natural versus induced flow connections

AAPG Rocky Mountain Section Meeting

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From Williston to the edge of the continental plate - a Rockies contrast in Mississippian-Devonian resource basin aspect ratio and natural versus induced flow connections

Abstract

Williston Basin is Over 1,000 miles from the western edge of the Devonian-Mississippian plate in central Nevada, yet there are many similarities in oil source and reservoir character but interesting contrasts in the progression of the resource to production. Williston Basin is located in a stable plate setting while the western plate edge has experienced major foldthrusting followed much later by the extensional basin and range formation during which reservoir blocks deposited near the Utah-Nevada border have been extended to be located 100 miles further west in central Nevada. Massive Devonian carbonates accumulated during varying eustacy resulting in cycles of dolomitization and degrees of anhydrite and varying siliceous content accumulated in each marine setting. After the major deposition of these source and reservoir intervals the history of the basins diverges. At the western edge of the plate three major compressional events from Mississippian through Jurassic resulted in folds and complex thrust stacking of the eventual petroleum system. The compressional events interrupted subsidence of these strata and any overlying formations were often eroded off during unconformity periods with exposure of the Paleozoic section to erosion and solution enhancement of faulted structures. The divergent history of the basins continued with the regional subsidence of the Williston Basin compared to the generation of multiple highaspect ratio basins formed as the resource shifted to its current location in central Nevada due to Tertiary and continuing extension. Thermal maturation of the thick organic-rich Mississippian Chainman source rocks awaited basin subsidence for oil generation. Oil generation in the central Nevada basins has been underway for only one tenth the period that oil has been generated from the similar source rocks of the Williston Basin. Two of the central Nevada basins, Railroad Valley Basin and Pine Valley Basin, will be presented with review of Grant Canyon and Blackburn Field contrast between each other and the Mississippian and Devonian of the Williston Basin.