--> --> Geological and Technological Components of Bakken and Three Forks Reservoirs, Williston Basin, USA

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Geological and Technological Components of Bakken and Three Forks Reservoirs, Williston Basin, USA

Abstract

The Bakken and Three Forks formations are productive across much of the Williston Basin. The first production dates back to 1953 with discoveries at the Antelope Field of North Dakota. The Bakken became an important horizontal target commencing in 2000 with the development of Elm Coulee Field in Montana. The Three Forks became a target from 2007 to the present. The USGS technically recoverable number for the Bakken and Three Forks is 7.5 billion barrels oil and 6,700 billion cubic feet of gas (USGS, 2013). Six distinct facies are present in the Bakken of the Williston Basin. Overall the succession appears to represent shelf deposits ranging from subtidal to lower intertidal back to subtidal. The amount of limestone, dolomite and sandstone present varies across the area. In general, more dolomite and limestone is present in the southern part of the basin and the siliciclastic content increases towards the north. The Three Forks consists largely of silty dolostone, clay-rich dolostones, red beds and anhydrites. These units were deposited in subtidal to supratidal environments in a restricted epeiric sea. Four regional units of the Three Forks have been identified and regional thicknesses and correlations established. The upper three cycles of the Three Forks are the current target of exploration. Recent cores of these intervals show significant residual oil saturation. Thus, petroleum potential in these units is high. The Bakken and Three Forks are regarded as technology reservoirs because they require horizontal drilling and multistage fracture stimulation. Some critical geologic components for the reservoirs include sedimentary facies, mineralogy, mechanical stratigraphy, diagenetic history, overpressure, source rock maturity, natural fractures and traps. Critical technology components include lateral length, number of hydraulic fracture stages, proppant volume and type, proppant loading, fluid volume and type, fluid to proppant ratio, injection rate, treatment pressure, choke size, plug and perf versus sliding sleeve completions, and well spacing.