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The U.S. Geological Survey (USGS) has estimated how much conventional oil and gas may still be undiscovered and technically recoverable in upper Paleozoic reservoirs of three geologic provinces: the Wind River Basin, the Bighorn Basin and the Powder River Basin.
The answer, in brief
| Mean estimate | Range (F95–F5) | |
|---|---|---|
| Oil | 47 million barrels | 24 to 76 million barrels |
| Gas | 876 billion cubic feet (0.9 trillion) | 198 to 2,186 billion cubic feet |
| Natural gas liquids | 20 million barrels | 4 to 50 million barrels |
F95 means a 95% chance of at least that amount; F5, a 5% chance.
The basins
All three are intermontane basins, formed during the Laramide orogeny (Late Cretaceous to Paleogene), when deformation reaching down into the basement broke up the Sevier foreland (Yeck and others, 2014; Yonkee and Weil, 2015).
| Era | Exploration |
|---|---|
| 1920s | drilling for oil in structural traps along the basin margins began in earnest — many of the folds and faults were plain to see at the surface |
| By the 1960s | most structural fields had been found |
| Since | the search turned to oil in complex stratigraphic and structural traps in the wind-deposited (eolian) sandstones of the Permian upper Minnelusa Formation, in the north-central Powder River Basin |
The five conventional assessment units. USGS
Where the oil came from, and where it went
The USGS grouped the resources into three total petroleum systems (TPS) — each a set of source rocks and the oil and gas they generated — and five assessment units (AUs).
Paleozoic–Mesozoic Composite TPS
Oil generated in thermally mature Pennsylvanian and Cretaceous organic-rich shales.
- Powder River Basin Leo Sandstone Reservoirs AU: oil from Pennsylvanian and Cretaceous shales (Clayton and Ryder, 1984) that moved into structural traps in the Hartville uplift, held mostly in eolian sandstone of the Pennsylvanian Leo Sandstone Member of the Minnelusa Formation.
Phosphoria TPS
Oil that may have come from organic-rich shales of the Retort Tongue and Meade Peak Member of the Permian Phosphoria Formation in west-central Wyoming and eastern Idaho (Maughan, 1975). Phosphoria oil ended up in upper Paleozoic reservoirs in all three provinces (Donohue and others, 2020), perhaps after a long migration eastward (Sheldon, 1967; Stone, 1967; Maughan, 1975) — though how and when it moved, relative to when the traps formed, is not well understood (Burtner and Nigrini, 1994; Ellis and others, 2017; Kendall and others, 2023).
- Wind River Basin and Bighorn Basin Upper Paleozoic Reservoirs AUs: Phosphoria oil in eolian sandstones of the Pennsylvanian Amsden Formation and the Pennsylvanian–Permian Tensleep Sandstone, and in Phosphoria carbonates, within Laramide-age traps.
- Phosphoria gas is thought to have formed at depth and been trapped mainly in carbonates of the Mississippian Madison Group — such as the hydrogen-sulfide-rich gas in Madison dolomites at the Madden Deep Field in the Wind River Basin (Hawkins and Baugh, 2006).
Pennsylvanian–Permian Composite TPS
Oil and gas from Phosphoria shales (Donohue and others, 2020), and perhaps oil from shales in the middle Minnelusa Formation (Clayton and Ryder, 1984; Desmond and others, 1984), in the Powder River Basin.
- Powder River Basin Minnelusa Sandstone Reservoirs AU: oil in Wolfcamp-age eolian sandstones in a range of stratigraphic and structural traps; also covers oil in middle-Minnelusa sandstones and oil and gas in Madison Group carbonates.
- Powder River Basin Tensleep Basin Margin Reservoirs AU: oil that migrated out of the basin into structural traps along its western and southern margins, in Tensleep sandstones and possibly Madison carbonates.
Results by assessment unit
Mean estimates, fully risked, split as the USGS reports them between oil accumulations and gas accumulations:
| Assessment unit | AU probability | Oil accumulations: oil / gas / NGL | Gas accumulations: gas / NGL |
|---|---|---|---|
| Powder River Basin Leo Sandstone | 0.95 | 2 / 1 / 0 | — |
| Wind River Basin Upper Paleozoic | 1.0 | 4 / 4 / 0 | 610 / 14 |
| Bighorn Basin Upper Paleozoic | 1.0 | 22 / 12 / 1 | 200 / 3 |
| Powder River Basin Minnelusa Sandstone | 1.0 | 15 / 1 / 0 | 47 / 2 |
| Powder River Basin Tensleep Basin Margin | 0.95 | 4 / 1 / 0 | — |
| Total | oil 47 · gas 876 · NGL 20 |
Oil and natural gas liquids (NGL) in million barrels; gas in billion cubic feet.
The Bighorn Basin holds the most undiscovered oil, and the Wind River Basin the most gas.
What went into the estimates
The model's key inputs were how many fields remain to be found and how big they are likely to be (more in Schenk, 2025):
| Assessment unit | Oil fields (min–median–max) | Gas fields (min–median–max) | Median oil field | Median gas field |
|---|---|---|---|---|
| Powder River Basin Leo Sandstone | 1–2–4 | — | 0.8 million barrels | — |
| Wind River Basin Upper Paleozoic | 1–4–12 | 1–12–48 | 0.8 million barrels | 18 billion cubic feet |
| Bighorn Basin Upper Paleozoic | 1–20–40 | 1–6–24 | 0.8 million barrels | 12 billion cubic feet |
| Powder River Basin Minnelusa Sandstone | 1–15–30 | 1–2–8 | 0.8 million barrels | 12 billion cubic feet |
| Powder River Basin Tensleep Basin Margin | 1–4–8 | — | 0.8 million barrels | — |
More results: the USGS Energy Resources Program.
Sources
Based on Schenk CJ, Mercier TJ, Le PA, Cicero AD, Drake RM II, Gelman SE, Hearon JS, Johnson BG, Lagesse JH, Leathers-Miller HM, Timm KK, "Assessment of Undiscovered Conventional Oil and Gas Resources in Upper Paleozoic Reservoirs of the Wind River Basin, Bighorn Basin, and Powder River Basin Provinces, 2024," U.S. Geological Survey Fact Sheet 2024–3049, U.S. Geological Survey; a work of the United States government in the public domain.
Licens: CC0 1.0 (allmän egendom) · Bearbetat efter pubs.usgs.gov
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