Shale Gas in the Phosphoria Formation of the Wyoming Thrust Belt: A USGS Assessment

U.S. Geological Survey Fact Sheet 2018–3001, National and Global Petroleum Assessment. By the Phosphoria Formation Assessment Team: Christopher J. Schenk, Tracey J. Mercier, Marilyn E. Tennyson, Cheryl A. Woodall, Thomas M. Finn, Janet K. Pitman, Stephanie B. Gaswirth, Kristen R. Marra, Phuong A. Le, Timothy R. Klett and Heidi M. Leathers-Miller.

Using its geology-based method, the USGS estimates mean undiscovered, technically recoverable resources of 198 billion cubic feet of continuous gas in the Phosphoria Formation of the Wyoming Thrust Belt Province, in Wyoming, Idaho and Utah.

The setting

The Wyoming Thrust Belt formed when east-directed compression, linked to steeply dipping subduction during the Sevier Orogeny (latest Jurassic to Late Cretaceous), stacked a series of thrust sheets, each younger to the east. The main thrusts are the Paris-Willard, Meade, Crawford, Absaroka, Hogsback-Darby and Prospect. The assessment asks how much shale gas could remain in Phosphoria shales after all that deformation.

The Phosphoria Shale Gas Assessment Unit in the Wyoming Thrust Belt Province. Base map from the National Park Service. USGS.

The source rocks

The USGS defined a Phosphoria Total Petroleum System and, within it, a Phosphoria Shale Gas Assessment Unit.

• The source is organic-rich shale of the Lower Permian Phosphoria Formation — the Meade Peak Member (up to 60 metres thick) and the Retort Tongue (up to 30 metres).
• They hold marine Type IIS organic matter, averaging 4 percent total organic carbon and reaching 13 percent.
• They are mostly dry-gas to overmature.
• Phosphoria-sourced condensate is known in the Tip Top, Dry Piney and Hogsback fields, and gas in the Phosphoria at Cave Creek (Utah), Whitney Canyon-Carter Creek, Yellow Creek and Thomas Canyon (Wyoming).

The geological model

• The shales reached the oil window under Mesozoic sediments before most thrusts formed.
• Much of their oil migrated east before thrusting, into traps in what are now the Laramide basins of Wyoming, Montana and Colorado.
• Any oil left in the shales cracked to gas as the stacking thrusts buried them deeper through the Sevier and Laramide deformations, putting them in the dry-gas or overmature window.
• The gas may carry a lot of hydrogen sulfide.
• The big uncertainty is how much oil stayed after migration, and how much gas survived thrusting.

Key inputs (minimum / most likely / maximum), from U.S. shale-gas analogues:

Results

F95 is a 95 percent chance of at least the amount shown. The zeros at F95 reflect the geological risk that no gas was retained in the shales.

Sources

• Schenk, C.J., and others, 2018, Assessment of continuous gas resources in the Phosphoria Formation of the Wyoming Thrust Belt Province, Wyoming, Idaho, and Utah: U.S. Geological Survey Fact Sheet 2018–3001. https://doi.org/10.3133/fs20183001 · https://pubs.usgs.gov/publication/fs20183001
• The map, the input and results tables and the assessment team come from the fact sheet's PDF.
• Rewritten in hubnx's own words.