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Influence of the Pronghorn Member of the Bakken Formation on the Drilling and Production Potential of the Upper Three Forks in McKenzie County, Williston Basin, North Dakota

Mark Millard, Murray Dighans, and Greg Hilton
SM Energy Company

The Pronghorn is a recently renamed member of the Bakken formation in the Williston Basin, North Dakota. Recent work by Johnson (2013) divided the pronghorn in 4 distinct facies across the Williston Basin. While the lower facies of the Pronghorn have been associated with recent production in the basin, the uppermost facies (Pronghorn Shale), described as grey shale with laminations of siltstone to fine-grained sandstone, appears to have a negative impact on production. The Pronghorn Shale is most prominent in central McKenzie County, reaching a maximum thickness of 35 ft. Mineralogical characteristics of the shale, predominately the large presence of clays, have a significant effect on the oil saturation and productivity of the underlying Three Forks. Wireline based maps, and recent production data aid in understanding the influence of Pronghorn Shale deposition on oil migration into the Upper Three Forks. Pronghorn deposition also had an influence on the deposition of the overlying Middle and Lower Bakken source and reservoir intervals. In addition, the presence of the Pronghorn Shale in Central McKenzie Co. introduces complications while attempting to set casing and drill horizontal wells in the Upper Three Forks. Specific examples, along with mitigation methods are also discussed in this presentation.

AAPG Search and Discovery Article #90169©2013 AAPG Rocky Mountain Section 62nd Annual Meeting, Salt Lake City, Utah, September 22-24, 2013