Analysis: Middle Three Forks Bench Holds Vast Untapped Oil Potential
Williston Basin operators have mostly landed laterals in the shallower upper Three Forks bench. But the deeper middle Three Forks contains hundreds of millions of barrels of oil yet to be recovered, North Dakota state researchers report.
The Bakken Shale is the most popular target in North Dakota oil country—but experts caution not to count out the deeper Three Forks formation.
In fact, the middle Three Forks reservoir still contains hundreds of millions of barrels of undeveloped recoverable oil, according to two studies recently published by the North Dakota Department of Mineral Resources.
Through August 2023, North Dakota producers have drilled and completed more than 400 horizontal wells in the middle (2nd) and lower (3rd) Three Forks intervals, producing more than 91 MMbbl of oil, 234 Bcf of natural gas and 106 MMbbl of water, according to the first study.
“These wells have amounted to ~2% of the drilling activity in the Bakken-Three Forks petroleum system, and ~1.7% of the total oil production to date,” authors Timothy Nesheim and Edward Starns wrote in the report.
Most of those projects (360+ wells) have landed in the shallower middle Three Forks bench.
Operators have only landed around 40 laterals in the deeper lower Three Forks. Just six lower Three Forks horizontals have come online since 2014—and none since 2017, “likely due to variable and overall low well production results,” per the report.
Lower Three Forks wells have produced approximately 6.7 MMbbl, 14 Bcf of gas and 11 MMbbl of water through August 2023.
Nesheim and Starns aimed to answer a key question in the first study: Does direct drilling and development of the middle Three Forks reservoir provide additional resource recovery? Or does middle Three Forks co-development only accelerate recovery rates of resources that would have otherwise been recovered by standalone upper Three Forks development?
“If middle Three Forks co-development simply accelerates oil and gas recovery rates, but does not add any long-term resource, then upper Three Forks wells should be less productive in the middle Three Forks co-development area versus upper Three Forks well performance where the middle Three Forks was not co-developed,” they wrote.
The report evaluated historical and future projected oil production from 593 North Dakota horizontal wells across 51 drilling spacing units (DSUs). North Dakota DSUs are typically 1,280 acres, or 2 square miles.
The study focused on northeastern McKenzie County, North Dakota—near the deepest portions of the Williston—where most of the middle Three Forks development has been sited.
Of the 25 DSUs evaluated that contained middle Three Forks horizontals, 17 “exhibited a clear volumetric addition of oil” from the reservoir, according to the study; six did not, and the contributions were unclear for two of the units.
Water-cut map of middle Three Forks horizontal wells based upon productive wells drilled and completed through the end of 2019. Middle Three Forks horizontal wells are represented by small black lines. The white outline denotes the main study area. The yellow star denotes the location of Enerplus Resource’s Hognose 152-94-18B-19H-TF. (Source: North Dakota Department of Mineral Resources)
Those 17 DSUs with middle Three Forks development showed an approximate 1 MMbbl to 2 MMbbl uplift in EURs compared to adjacent units without middle Three Forks development.
The first study aimed to demonstrate the incremental productivity of co-developing the middle Three Forks alongside the middle Bakken and upper Three Forks. A second study aimed to define a contiguous area of potential new development for middle Three Forks projects.
Assuming middle Three Forks wells can be drilled in each 1,280-acre DSU, researchers outlined approximately 275,000 acres in northeast McKenzie County where new horizontal wells are most viable.
Not counting existing wells, 604 middle Three Forks horizontals could still be drilled with that immediate prospective area, according to the study. Ultimate EURs for the new projects could range between 165 MMbbl and 410 MMbbl of oil.
“The results of these studies indicate that developing the middle Three Forks in addition to the Middle Bakken and upper Three Forks can increase long-term recovery,” Nesheim and Starns wrote.
With the Bakken shale in a later stage of maturity today, some North Dakota producers are touting their future upside in the deeper Three Forks intervals.
The Grayson Mill acquisition deal added 500 gross undrilled locations and around 300 candidates for refrac projects. Around 80% of the new locations are in the Bakken and 20% were underwritten in the Three Forks.
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