What was assessed
The U.S. Geological Survey assessed the remaining coalbed gas in the Vermejo and Raton Formations of the Raton Basin–Sierra Grande Uplift Province, in Colorado and New Mexico. A major pipeline arrived in the basin in the early 1990s, leading to more than 4,300 coalbed gas wells, which mapped out the most productive areas, or fairways. This assessment covers what remains, in the fairways and in outlying coal-bearing areas.
Figure 1. Location of the four assessment units; the Vermejo Formation units and the Raton Formation units. USGS.
Geology
The Raton Basin today is an intermontane basin, formed by Laramide mountain building in the latest Cretaceous and Paleogene. Before that it lay in the Sevier foreland basin, on the eastern side of the Cretaceous Western Interior Seaway.
- Vermejo Formation — with the underlying Trinidad Sandstone, a wave-dominated delta and barrier system on the seaway's eastern shore. Its coals formed in peat swamps behind the barriers and are laterally continuous, parallel to the old coastline.
- Raton Formation — deposited after Laramide uplift and erosion, beginning with a conglomerate carried by rivers flowing east from the rising mountains, then meandering rivers with broad floodplains. Its coals formed in swamps between river channels and are less continuous.
Assessment units
All four units belong to the Upper Paleozoic–Cenozoic Total Petroleum System:
| Unit | Defined by |
|---|---|
| Vermejo Formation Fairway and Raton Formation Fairway | more than 20 feet of net coal, bounded on the west by the Sangre de Cristo thrust belt |
| Vermejo Formation Outlying and Raton Formation Outlying | less than 20 feet of net coal, out to the "zero" gas line, which closely follows the outcrop of the Trinidad Sandstone |
The Vermejo units include Vermejo coals and Cretaceous coals in the lower Raton; the Raton units cover coals higher in the Raton. All four allow for gas from neighboring river sandstones produced along with coalbed gas through the usual vertical wells and hydraulic fracturing, and for gas that may have migrated up from fractured organic-rich shales — the Graneros Shale, Niobrara Formation and Sharon Springs Member of the Pierre Shale.
Results
The mean estimate of remaining coalbed gas is 5,210 billion cubic feet (5.2 trillion), with an F95–F5 range of 1,560 to 9,253 billion. (F95 is a 95 percent chance of at least that amount; F5 a 5 percent chance.)
| Unit | Mean gas (billion cubic feet) |
|---|---|
| Vermejo Formation Fairway | 1,827 |
| Vermejo Formation Outlying | 420 |
| Raton Formation Fairway | 2,441 |
| Raton Formation Outlying | 522 |
Results are also on the USGS Energy Resources Program website.
Sources
Based on Raton Basin–Sierra Grande Uplift Province Assessment Team, "Assessment of coalbed gas resources in the Raton Basin–Sierra Grande Uplift Province, Colorado and New Mexico, 2022," U.S. Geological Survey Fact Sheet 2023–3020; a work of the United States government in the public domain. It cites Osterhout and others (2015), Flores and others (1985), Higley (2007), Tremain (1980), Tyler and others (1995), Carlton (2006), Jurich and Adams (1984), Seidel (2002), Hoffman and Brister (2003), Woodward (1983, 1997) and Schenk (2023). The fact sheet names the outlying units "Outerlying"; this page uses "Outlying". Its table of input data is left out.
Licence: CC0 1.0 (public domain) · Adapted from pubs.er.usgs.gov
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