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U.S. Geological Survey, National and Global Petroleum Assessment. Fact Sheet 2020–3047, November 2020.
The result: a mean of 39 trillion cubic feet of undiscovered, technically recoverable gas, in continuous and conventional reservoirs of the Fruitland Total Petroleum System (TPS) in the San Juan Basin, New Mexico and Colorado.
Background
The assessment covers the Pictured Cliffs Sandstone, the Fruitland Formation and the Tertiary sandstones above them. The USGS last assessed the Fruitland TPS in 2002 (Ridgley and others, 2013). Since then, drilling has focused on the Fruitland's coal beds and tight-gas reservoirs in the Pictured Cliffs.
The rocks
These formations record the last major retreat of the sea from the San Juan Basin in the Cretaceous:
| Unit | Rock | Role |
|---|---|---|
| Pictured Cliffs Sandstone | very fine to medium sandstone, siltstone, mudstone, laid down at the sea's edge | reservoir |
| Fruitland Formation | interbedded coal, shale, siltstone and sandstone from coastal swamps | its coal beds are the main gas source; gas may also have moved up from the Lewis Shale below |
| Tertiary sandstones — Paleocene Ojo Alamo and Nacimiento, Eocene San Jose | mostly river conglomerate, sandstone, mudstone and shale | minor conventional gas |
The TPS takes in all the Cretaceous and Tertiary strata holding gas from Fruitland coals.
Figure 1: the San Juan Basin Province and the four assessment units. Base map from the National Park Service. USGS.
Four assessment units
| Unit | Type | Defined by |
|---|---|---|
| Pictured Cliffs Continuous Gas | continuous | the formation's extent in the basin |
| Basin Fruitland Coalbed Gas | continuous (coalbed) | the formation's extent in the basin |
| Northern Fruitland Coalbed Gas | continuous (coalbed) | the north, where artesian overpressure and heavy gas and water production occur |
| Tertiary Conventional Gas | conventional | the extent of the Tertiary sandstones |
Key inputs
Table 1. Minimum / mode / maximum (mean). Drainage area, success ratio and estimated ultimate recovery (EUR) partly follow U.S. shale-gas analogs.
| Input | Pictured Cliffs | Basin Fruitland Coalbed | Northern Fruitland Coalbed |
|---|---|---|---|
| Potential production area (acres) | 100,000 / 2,172,000 / 4,255,000 (2,175,667) | 10,000 / 1,800,000 / 3,462,000 (1,757,333) | 50,000 / 450,000 / 792,100 (430,700) |
| Drainage area per well (acres) | 40 / 80 / 160 (93.3) | 60 / 80 / 160 (100) | 60 / 80 / 160 (100) |
| Area untested (%) | 74 / 87 / 94 (85) | 78 / 89 / 92 (86.3) | 30 / 50 / 65 (48.3) |
| Success ratio (%) | 50 / 70 / 90 (70) | 50 / 70 / 90 (70) | 80 / 90 / 95 (88.3) |
| Average EUR (billion cubic feet) | 0.6 / 1.1 / 1.7 (1.122) | 0.6 / 1 / 1.5 (1.019) | 4 / 6 / 7 (6.019) |
| Unit probability | 1.0 | 1.0 | 1.0 |
Tertiary Conventional Gas: 1 / 3 / 5 undiscovered gas fields (mean 3.0), of 3 / 10 / 50 billion cubic feet each (mean 11.4); probability 0.9.
Results
Table 2: fully risked. F95 means a 95-percent chance of at least that amount; F5, a 5-percent chance.
| Unit | Gas, billion cubic feet: F95 | F50 | F5 | Mean | NGL, million barrels: mean (F95–F5) |
|---|---|---|---|---|---|
| Pictured Cliffs | 5,056 | 15,340 | 31,188 | 16,365 | 49 (13–103) |
| Basin Fruitland Coalbed | 3,331 | 10,730 | 20,449 | 11,156 | 0 |
| Northern Fruitland Coalbed | 4,080 | 10,928 | 20,652 | 11,481 | 0 |
| All continuous | 12,467 | 36,998 | 72,289 | 39,002 | 49 |
| Tertiary Conventional | 0 | 32 | 55 | 31 | 0 |
| Total | 12,467 | 37,030 | 72,344 | 39,033 | 49 (13–103) |
Most of the gas is in the three continuous units of the Pictured Cliffs and Fruitland.
Sources
Based on Assessment of Undiscovered Gas Resources of the Fruitland Total Petroleum System in the San Juan Basin, New Mexico and Colorado, 2020, USGS Fact Sheet 2020–3047, by the Fruitland Total Petroleum System Assessment Team: Kristen R. Marra, Christopher J. Schenk, Tracey J. Mercier, Heidi M. Leathers-Miller, Marilyn E. Tennyson, Thomas M. Finn, Cheryl A. Woodall, Michael E. Brownfield, Phuong A. Le and Ronald M. Drake II, U.S. Geological Survey; a work of the United States government in the public domain. The map and both tables are taken from the fact sheet's PDF, which the import had left out. Methods and data: USGS Energy Resources Program.
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