AAPG Annual Convention and Exhibition

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The Three Forks and Pronghorn in McKenzie Co., ND: More Than a Simple ‘Basin Centered Oil Accumulation’


Basin centered oil accumulations have played a significant role in the exploration of hydrocarbons in North America in recent years. The large-scale development of resource plays (“feeding the rig” and “drilling to hold acreage”) often leads to an oversimplified geological understanding of key play elements. The interaction between the Pronghorn member of the Bakken Formation and the underlying Three Forks in North Dakota provides a great example of how continuously updating geological models can lead to improved understanding and lower risk in basin centered oil accumulations. The Pronghorn is a recently renamed member of the Bakken formation in the Williston Basin, North Dakota. The presence of the uppermost facies, described as grey shale with laminations of siltstone to fine-grained sandstone, has a negative impact on production of the underlying Three Forks Formation. A combination of various data types aids in understanding the influence of Pronghorn deposition on oil migration into the Upper Three Forks. In addition, Pronghorn deposition had an influence on the depositional patterns of the Middle and Lower Bakken source and reservoir intervals, which in turn negatively affects their potential. Also discussed in this talk are key drilling concerns associated with drilling near the pronghorn.