Undiscovered Unconventional Oil and Gas in the Gulf Coast's Smackover Formation

The seven continuous assessment units in the Smackover Formation, onshore Gulf Coast. Map: U.S. Geological Survey.

The U.S. Geological Survey (USGS) has estimated the undiscovered, technically recoverable continuous (unconventional) oil and gas in the Smackover Formation, which runs along the Gulf Coast from the U.S.–Mexico border in Texas east to the Florida panhandle. Its mudstones are thought to be a major petroleum source rock for the Upper Jurassic–Cretaceous–Tertiary Composite Total Petroleum System of the Gulf Coast.

The estimate

F95 is a 95 percent chance of at least the amount given; F5 is defined the same way. The results are fully risked.

The rock

The Smackover was laid down on a carbonate ramp, a gently inclined carbonate surface running from the Oxfordian shoreline to the deep basin.

• Outer ramp: mainly subtidal mudstones. Laminated mudstones in its condensed section are often rich in organic matter, but they have rarely been explored as self-sourced shale-oil or shale-gas reservoirs.
• Inner ramp: from similar subtidal mudstones to high-energy intertidal and supratidal carbonates. Most conventional Smackover oil and gas fields are in these inner-ramp carbonates.

Seven assessment units

The USGS defined seven continuous assessment units, five for gas and two for oil. Their boundaries reflect:

1. how inner- and outer-ramp rock types vary in space and time, which affects how thick the potential source interval is;
2. peripheral faults or salt basins, which may have affected whether petroleum migrated or stayed put;
3. thermal maturity, which determines where oil rather than gas formed: oil units lie between 0.6 and 1.3 percent vitrinite reflectance, gas units beyond 1.3 percent;
4. sandstones in the Smackover delivered by the ancestral Mississippi River, found in parts of northern Louisiana, central Mississippi, southern Alabama and the far western Florida panhandle, which may form conventional reservoirs or migration paths and may dilute source-rock quality;
5. a maximum depth to the top of the formation of 46,000 feet, and limits of 230 degrees Celsius or 25,000 pounds per square inch, set by what current drilling and completion technology can handle, since the USGS assesses only resources recoverable with technology of the time.

Inputs and results by unit

Mean values. EUR is estimated ultimate recovery, in million barrels of oil (MMBO) or billion cubic feet of gas (BCFG).

Every unit's area is entirely untested, and each has a probability of 1.0.

Few wells to go on. Only 41 wells along the U.S. Gulf Coast have targeted the lower Smackover, and just 3 have enough production data to calculate EURs. So the assessors used earlier USGS assessments of Upper Jurassic rocks in northeast Mexico as guides for likely EURs.

Sources

• Whidden KJ, Birdwell JE, Gardner R, Kinney SA, Paxton ST, Pitman JK, Schenk CJ. "Assessment of continuous oil and gas resources in the Upper Jurassic Smackover Formation of the onshore U.S. Gulf Coast, 2022." U.S. Geological Survey Fact Sheet. https://pubs.er.usgs.gov/publication/fs20233021/full
• Input data: Schenk and Whidden (2023). The fact sheet also cites Mancini and others (2019), Snedden and Galloway (2019), Salvador (1991) and Schenk and others (2014); John W. Snedden of the University of Texas at Austin supplied the mapped extent of the ancestral Mississippi River sandstones.