Monday, 16 June, 2025/ Edition 63

This week, we will look at several new resources and studies discussing the potential for onshore exploration in the United States. First, let’s dive into some recent U.S. Geological Survey reports on the subject.

Rasoul Sorkhabi

Editor, Core Elements

USGS Assessment of Oil and Gas Resources

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The U.S. Geological Survey recently published five fact sheets about its assessment of undiscovered oil and gas resources in several key onshore formations.

#1 Gulf Coast Travis Peak and Hosston Formations

States: Texas, Louisiana, Mississippi, Alabama, Florida, Georgia

Sedimentology: Clastic sandstones deposited during marine transgression

Stratigraphy: Lower Cretaceous Travis Peak Formation in Texas correlatable to Hosston Formation in Louisiana

Total undiscovered conventional resources (mean): 28 million barrels of oil and 959 billion cubic feet of gas

Total undiscovered continuous resources (mean): 34,842 billion cubic feet of gas

Go deeper: USGS Fact Sheet 2025–3021

#2 Western Gulf Basin San Miguel, Olmos, and Escondido Formations

State: Texas

Sedimentology: The San Miguel, Olmos, and Escondido Formations were deposited atop a continental margin in a continental-to-deep-marine environment.

Stratigraphy: Upper Cretaceous sandstone with porosity of up to 15–20 percent and within mainly stratigraphic traps. The source rock is the Eagle Ford Shale.

Total undiscovered conventional resources (mean): 5 million barrels of oil and 25 billion cubic feet of gas

Go deeper: USGS Fact Sheet 2025–3015

#3 Upper Paleozoic Formations of Wind River, Bighorn River, and Powder River Basins

State: Wyoming

Sedimentology: These basins formed during the Late Cretaceous to Paleogene Laramide Orogeny and contain Paleozoic and Mesozoic sediments.

Stratigraphy: Various Mississippian to Permian formations. Reservoirs include Leo/Minnelusa Sandstone, Amsden Formation, Tensleep Sandstone, and Phosphoria Carbonates. Source rocks include Phosphoria and Madison.

Total undiscovered conventional resources of Powder River Basin Minnelusa Sandstone (mean): 15 million barrels of oil and 1 billion cubic feet of gas

Total undiscovered conventional resources of Powder River Basin Tensleep Sandstone (mean): 4 million barrels of oil and 1 billion cubic feet of gas

Total undiscovered conventional resources of Powder River Basin Leo Sandstone (mean): 2 million barrels of oil and 1 billion cubic feet of gas

Total undiscovered conventional resources of Wind River Basin Upper Paleozoic reservoirs (mean): 4 million barrels of oil and 4 billion cubic feet of gas

Total undiscovered conventional resources of Bighorn Basin Upper Paleozoic reservoirs (mean): 22 million barrels of oil and 12 billion cubic feet of gas

Go deeper: USGS Fact Sheet 2024–3049

#4 Mowry Formation

States: Wyoming, Colorado, and Utah

Sedimentology: The Mowry Shale is a marine, organic-rich, siliceous shale with a total organic carbon content of as much as five percent.

Stratigraphy: The Mowry Petroleum System consists of Lower Cretaceous Cloverly Sandstone, Dakota Sandstone, Thermopolis Shale, Muddy Sandstone, Shell Creek Shale, Upper Cretaceous Mowry Shale, and the Frontier Formation.

Total undiscovered conventional oil and gas resources (mean): 20 million barrels of oil and 112 billion cubic feet of gas

Total undiscovered continuous oil and gas resources (mean): 453 million barrels of oil and 27,193 billion cubic feet of gas

Go deeper: USGS Fact Sheet 2025–3023

#5 Monterey Formation

State: California (Los Angeles Basin)

Sedimentology: Organic-rich shale with total organic carbon values (TOC) as much as 17 percent, kerogen type II and III

Stratigraphy: Miocene Monterey Formation

Total undiscovered conventional resources (mean): 50 million barrels of oil and 199 billion cubic feet of gas

Total undiscovered continuous resources (mean): 11 million barrels of oil and 41 billion cubic feet of gas

Go deeper: USGS Fact Sheet 2024–3051

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Petroleum Charge in the Marietta Basin, Oklahoma

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Geologists from The University of Oklahoma published a recent study offering important information on the Marietta Basin.

Why it matters: The Marietta Basin, unlike the neighboring and well-studied Anadarko Basin, is a frontier for exploration and shale development.

About the basin: The Marietta Basin, a narrow syncline trending northwest-southeast, is one of Oklahoma’s smallest and least-known basins.

Study design:

• Thirty-three samples from the Woodford Shale were analyzed for Rock-Eval pyrolysis and TOC.

• Of these core samples, 13 were subjected to vitrinite reflectance (VR) measurements.

• Additionally, GS and GS-MS analyzed hydrocarbon extracts from 10 core samples.

Results:

• The Woodford has excellent source rock potential, with TOC values of 2.9 to 9.8 percent, VR values of 0.73 to 0.85 percent, and kerogen type II.

  • Hydrogen index values indicate marine oil prone source rock. Woodford Top in the basin ranges from 5,000 to 17,000 feet.

• Geochemical signatures of oil show that while some oils were charged from Upper Devonian Woodford Shale, many oils are mixtures charged from Woodford Shale and Ordovician Viola carbonates. Evidence for Viola carbonates came from data sourced in the nearby Anadarko Basin.

Go deeper: Read the full article here.

A message from AAPG Academy and the Energy Minerals Division

Join AAPG Academy and AAPG's Energy Minerals Division (EMD) on 17 June at 9am CDT as we explore the emerging trends and developments that are making a difference in the quest for critical minerals and rare earth elements.

Our conversation will be led by two expert speakers, Ashley Douds and Aaron Ball, who are the president and president-elect of AAPG's Energy Minerals Division, respectively.

Douds will begin by examining recent trends in energy minerals with a focus on the state of Indiana and the Appalachian Basin. She will be followed by Ball, who will take an even closer look, analyzing brines with laser-induced break spectroscopy and how they can be used to predict the presence of light and heavy elements.

Recommended Reading

Photo source: Amazon.com

A new book, American Heat Engine: Hydrocarbons and the Power of the United States, blends industry and U.S. history into one narrative.

Author: Kent Williamson worked for IHS Markit (merged with S&P Global in 2022) for years. He spent the last three years writing this book.

Content: Through 10 chapters, 380 pages, and 15 maps, the book takes readers on a historical and geographic journey from the coal state of Virginia and oil state of Pennsylvania in the 19th century, to Texas during the shale revolution of the 21st century. It shows how coal, oil, and gas have powered economic development, helped win world wars, and fueled various industries.

Why it matters: As scientists, we are usually concerned with the geology of resources. This book provides a historical, economic, and political perspective on these resources.  

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✉️ To get in touch with Rasoul, send an email to editorial@aapg.org.