Abstract

The Devonian Sanish pool is on the steep northeast flank of the Antelope anticline in the central Williston basin. Unique features--high productivity from wells in the dolomite-shale facies of the 'Sanish Sand' zone, very high initial reservoir pressure, and almost complete absence of water production--suggest that productivity is a function of tension fracturing. Fracture porosity varies directly as the product of bed thickness times structural curvature, and fracture permeability varies as the third power of this product. The overlying Bakken Shale is the immediate, and ultimate, oil source; the Sanish fracture system gathers the oil. Very high initial reservoir pressure indicates that Sanish-Bakken accumulation is in an isolated, oil-saturated reservoir independent of structure in the normal sense. The Bakken Shale beds are believed to be everywhere oil saturated.

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