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U.S. Geological Survey, National and Global Petroleum Assessment. Fact Sheet 2020–3048, November 2020.
The result: a mean of 2.6 trillion cubic feet of undiscovered, technically recoverable continuous (unconventional) gas in the Lewis Shale Total Petroleum System of the San Juan Basin, New Mexico and Colorado.
Background
The USGS last assessed the Lewis Shale in 2002, as part of a broader look at the basin's Jurassic and Cretaceous reservoirs (Dubiel, 2013). Its gas comes mainly from:
- shoreface sandstones of the Cliff House Sandstone;
- recompleted Mesaverde Group wells reaching the Lewis Shale's marine rocks — gas that is commingled with Lewis Shale production.
Figure 1: the San Juan Basin Province and the three assessment units. Base map from the National Park Service. USGS.
The rocks
- Setting: laid down in the Cretaceous Western Interior Seaway.
- Makeup: offshore marine shale, mudstone, siltstone and sandstone, interfingering to the southwest with the Cliff House Sandstone's La Ventana and Chacra tongues (part of the Mesaverde Group).
- Layers: the Otero and Navajo City intervals below the Huerfanito Bentonite Bed — a distinct volcanic ash marker — and the Ute interval above it, laid down at the peak of the sea's advance in the Campanian.
- Top: grades up into the shoreface sands of the Pictured Cliffs Sandstone.
- Thickness: up to about 2,400 feet, in the basin's northeast.
Where the gas came from: the shale is self-sourced. Its organic-rich marine rock (Type II kerogen) was buried deep enough to generate gas during the Oligocene, with Type III organic matter washed in by rivers and deltas from the southwest. Gas moved a short distance into the Cliff House sandstones.
Three assessment units
| Unit | Covers |
|---|---|
| Lewis Shale Continuous Gas | the shale from the deepest central basin to its northeastern limit |
| Lewis–Cliff House Continuous Gas | the shale's southwestern extent, plus production from the Chacra and La Ventana sandstone trends to the south |
| Cliff House Fairway Continuous Gas | bounded on the northeast by the New Mexico Oil Conservation Division's pool line for the Chacra interval, and on the southwest by established production in its shelf 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. Each unit's probability is 1.0.
| Input | Lewis Shale | Lewis–Cliff House | Cliff House Fairway |
|---|---|---|---|
| Potential production area (acres) | 50,000 / 800,000 / 1,900,000 (916,667) | 1,000 / 500,000 / 2,187,000 (896,000) | 50,000 / 400,000 / 719,000 (389,667) |
| Drainage area per well (acres) | 80 / 120 / 160 (120) | 80 / 120 / 160 (120) | 80 / 120 / 160 (120) |
| Area untested (%) | 96 / 97 / 99 (97.3) | 98 / 99 / 100 (99) | 70 / 80 / 90 (80) |
| Success ratio (%) | 50 / 70 / 90 (70) | 40 / 50 / 70 (53.3) | 70 / 80 / 90 (80) |
| Average EUR (billion cubic feet) | 0.18 / 0.2 / 0.5 (0.216) | 0.07 / 0.1 / 0.18 (0.104) | 0.3 / 0.5 / 0.8 (0.512) |
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) |
|---|---|---|---|---|---|
| Lewis Shale | 361 | 1,066 | 2,112 | 1,133 | 2 (1–5) |
| Lewis–Cliff House | 102 | 374 | 853 | 414 | 0 (0–1) |
| Cliff House Fairway | 419 | 1,053 | 1,808 | 1,076 | 1 (1–3) |
| Total | 882 | 2,493 | 4,773 | 2,623 | 3 (2–9) |
Sources
Based on Assessment of Undiscovered Gas Resources in the Lewis Shale Total Petroleum System of the San Juan Basin Province, New Mexico and Colorado, 2020, USGS Fact Sheet 2020–3048, by the Lewis Shale 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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