By the USGS Eagle Ford Group Assessment Team: Katherine J. Whidden, Janet K. Pitman, Ofori N. Pearson, Stanley T. Paxton, Scott A. Kinney, Nicholas J. Gianoutsos, Christopher J. Schenk, Heidi M. Leathers-Miller, Justin E. Birdwell, Michael E. Brownfield, Lauri A. Burke, Russell F. Dubiel, Katherine L. French, Stephanie B. Gaswirth, Seth S. Haines, Phuong A. Le, Kristen R. Marra, Tracey J. Mercier, Marilyn E. Tennyson and Cheryl A. Woodall
The upper Eagle Ford Group at Lozier Canyon, near Del Rio, Texas. Photo: Stanley T. Paxton, USGS.
Using a geology-based method, the U.S. Geological Survey estimated undiscovered, technically recoverable resources in continuous accumulations of the Upper Cretaceous Eagle Ford Group and associated Cenomanian–Turonian strata, onshore in the U.S. Gulf Coast region of Texas: a mean of 8.5 billion barrels of oil and 66 trillion cubic feet of gas.
The rocks
The Eagle Ford holds one of the most prolific continuous oil and gas accumulations in the United States.
- What it is: mostly mudstone and calcareous mudstone (marl), with organic-rich intervals.
- Where it formed: in outer shelf and upper slope seas during the Cenomanian–Turonian ages (Denne and Breyer, 2016).
- What else was assessed: mudstones that may be slightly older than the Eagle Ford but are poorly understood in age and extent — the "associated Cenomanian–Turonian strata."
- The dividing line: to capture how the resource varies, Eagle Ford marl is defined as under 25 percent clay, and Cenomanian–Turonian mudstone as over 25 percent (Donovan and others, 2017).
They are part of the Upper Jurassic–Cretaceous–Tertiary Composite Total Petroleum System (Dubiel and others, 2012). The USGS assesses such systems by their source rock — its thickness, organic richness and thermal maturity — and divides them into assessment units (AUs) of rock with similar structural and charge histories, lithology and stratigraphy.
The seven assessment units of the Eagle Ford Group and associated Cenomanian–Turonian strata. USGS.
Seven assessment units
The seven AUs were drawn by lithology, thickness, thermal maturity, regional geologic features, and where the productive fairways lie.
| AU | Bounded by |
|---|---|
| Eagle Ford Marl Continuous Oil | the U.S.–Mexico border, the 25-percent-clay line, and the oil window (0.6–1.3 percent modeled vitrinite reflectance) |
| Submarine Plateau–Karnes Trough Continuous Oil | within the marl oil unit, where the Eagle Ford is thicker than 120 feet (Hammes and others, 2016) — more source rock and reservoir |
| Cenomanian–Turonian Mudstone Continuous Oil | the 25-percent-clay line, the eastern limit of Cenomanian–Turonian oil production (about the Texas–Louisiana line), and the oil window |
| Eagle Ford Marl Continuous Gas | the U.S.–Mexico border, the 25-percent-clay line, the updip limit of gas (1.3 percent vitrinite reflectance), and the Lower Cretaceous shelf margin (Donovan and others, 2015) |
| Submarine Plateau–Karnes Trough Continuous Gas | within the marl gas unit, where the Eagle Ford is thicker than 120 feet |
| Cenomanian–Turonian Mudstone Continuous Gas | the 25-percent-clay line, the updip limit of gas, and the Upper Cretaceous shelf margin (Galloway, 2008) |
| Cenomanian–Turonian Downdip Continuous Gas | out to the State–Federal waters boundary — not assessed, for lack of data |
Inoceramid shells on a bedding plane in the USGS Gulf Coast #1 West Woodway research core through the Eagle Ford Group, drilled near Waco, Texas. Photo: Stanley T. Paxton, USGS.
The estimates
For the six assessed units, the mean estimates are:
- Oil: 8,515 million barrels — about 8.5 billion (F95–F5 range 5,266 to 12,846).
- Gas: 65,981 billion cubic feet — about 66 trillion cubic feet (37,984 to 104,048).
- Natural gas liquids: 1,891 million barrels (1,032 to 3,093).
F95 means a 95-percent chance of at least that much; F5, a 5-percent chance.
| AU | Oil, mean (million barrels) | Gas, mean (billion cubic feet) |
|---|---|---|
| Eagle Ford Marl (oil) | 5,129 | 10,240 |
| Cenomanian–Turonian Mudstone (oil) | 3,204 | 6,412 |
| Submarine Plateau–Karnes Trough (oil) | 182 | 546 |
| Eagle Ford Marl (gas) | — | 35,304 |
| Submarine Plateau–Karnes Trough (gas) | — | 8,100 |
| Cenomanian–Turonian Mudstone (gas) | — | 5,379 |
Among the biggest: these results rank among the top five continuous oil and gas resources the USGS has assessed in the United States.
The top five USGS continuous oil and gas assessments through 2018 (Coleman and others, 2011; Kirschbaum and others, 2012; Gaswirth and others, 2013, 2016; Marra and others, 2015, 2017; Hawkins and others, 2016; Paxton and others, 2017a, b). USGS.
More: USGS Energy Resources Program.
Sources
Based on Assessment of Undiscovered Oil and Gas Resources in the Eagle Ford Group and Associated Cenomanian–Turonian Strata, U.S. Gulf Coast, Texas, 2018, by the Eagle Ford Group Assessment Team, USGS Fact Sheet 2018–3033, U.S. Geological Survey; a work of the United States government in the public domain. The import had kept only the fact sheet's references; its text, figures, photographs and results are taken from the PDF.
Licence: CC0 1.0 (public domain) · Adapted from pubs.usgs.gov
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