Tight Oil in Utah's Uteland Butte: USGS Assessment of the Uinta Basin, 2015

Summary

Using a geology-based method, the U.S. Geological Survey estimated the undiscovered oil and gas in the informal Uteland Butte member of the Eocene Green River Formation, Uinta Basin, Utah. Mean estimates:

• 214 million barrels of oil;
• 329 billion cubic feet of associated and dissolved gas;
• 14 million barrels of natural gas liquids.

Successful tight oil development in the Uteland Butte, with horizontal drilling and hydraulic fracturing, has renewed interest in the oil potential of lake-deposited rocks.

The Uinta-Piceance Basin Province and the Uteland Butte assessment units. USGS; base from the National Park Service.

Two assessment units

The USGS defined a Green River Total Petroleum System with two assessment units.

Uteland Butte Carbonate Continuous Oil

• Covers much of the deep central basin: organic-rich offshore lake carbonate and shale.
• The best reservoir, and the main horizontal-drilling target, is dolomite — highly porous but nearly impermeable. Significant oil also lies in the neighboring organic-rich shale and fine-grained limestone.
• A sweet spot of unusually high recoveries per well lies in the north-central part, where formation pressures are abnormally high. Overpressure — mapped from drilling-mud weights and drill-stem tests — is the best predictor of production. Other factors: total thickness of the member, thickness of the dolomite beds, organic richness and thermal maturity.

Uteland Butte Conventional Oil and Gas

• Sandstone, siltstone, carbonate and mudstone laid down at the lake's margins, filled with oil that migrated from the mature offshore rocks.
• North area: along the deep basin trough, where maturity is high and overpressure occurs locally. Oil is trapped where the margin reservoirs pinch out updip into the offshore carbonate and shale.
• South area: along the south margin, where maturity is low and pressures near normal; traps are probably margin sandstones pinching out into alluvial mudstone.
• Mostly undiscovered oil fields, with some gas likely: gas has migrated upward from deeper Upper Cretaceous source rocks and may be trapped where there is a seal.

Results (means)

Sources

Based on "Assessment of Undiscovered Oil and Gas Resources in the Uteland Butte Member of the Eocene Green River Formation, Uinta Basin, Utah, 2015," U.S. Geological Survey fact sheet; a work of the United States government in the public domain. The map is taken from the fact sheet's PDF.