By the USGS Cuyo Basin Province Assessment Team: Christopher J. Schenk, Michael E. Brownfield, Marilyn E. Tennyson, Phuong A. Le, Tracey J. Mercier, Thomas M. Finn, Sarah J. Hawkins, Stephanie B. Gaswirth, Kristen R. Marra, Timothy R. Klett, Heidi M. Leathers-Miller and Cheryl A. Woodall
Using a geology-based method, the U.S. Geological Survey estimated undiscovered, technically recoverable oil and gas — both continuous (unconventional) and conventional — in the Cuyo (or Cuyana) Basin Province of Argentina.
The Cuyo Basin Province and its three assessment units (AUs); the Alvear unit was not assessed. USGS.
How the basin formed
- Triassic: as South America began to pull away from Africa, the crust stretched into a group of subbasins (Uliana and others, 1989; Milani and Fihlo, 2000; Barredo, 2012; Barredo and others, 2012). They filled with everything from volcanic rock to river and lake sandstones and shales.
- Middle Triassic: organic-rich lake shales of the Cacheuta Formation — the province's source rock — were laid down (Lopez-Gamundi, 2010; Legarreta and Villar, 2011).
- Miocene: Andean compression inverted many of the old rift structures (Dellape and Hegedus, 1995). The wedge of sediment shed from the rising mountains buried the Cacheuta subbasin's shales into the oil window in the late Miocene to Pliocene.
The source rock
The Triassic Cacheuta Lacustrine Total Petroleum System is defined by the Cacheuta shales:
- up to 400 meters thick;
- mostly Type I organic matter;
- up to 10 weight percent organic carbon (Legarreta and Villar, 2011);
- mature for oil in the Cacheuta subbasin, where nearly all the conventional oil fields are.
Three assessment units
| Unit | Idea | Assessed? |
|---|---|---|
| Cacheuta Subbasin Lacustrine Shale Oil | some recoverable oil stayed in the shales after the rest migrated into conventional traps | yes |
| Cacheuta Subbasin Conventional Oil | oil that migrated from the shales into river and lake sandstones of the rift, and river sandstones of the overlying Rio Blanco Formation, within inverted Triassic structures | yes |
| Alvear Subbasin Lacustrine Shale Oil | the Alvear subbasin's shales are generally thought too immature to have made oil (Pucci, 2013) | no — too uncertain |
For the shale-oil unit, well drainage areas, estimated ultimate recoveries and success ratios were guided by U.S. shale-oil analogs.
The estimates
Mean estimates of undiscovered, technically recoverable resources, with F95–F5 ranges (F95: a 95-percent chance of at least that much; F5: a 5-percent chance):
| Oil (million barrels) | Gas (billion cubic feet) | |
|---|---|---|
| Shale oil (continuous) | 215 (45–498) | 108 |
| Conventional | 21 (10–39) | 4 |
| Total | 236 (55–537) | 112 (23–266) |
Natural gas liquids: a mean of 1 million barrels (0–2).
More: USGS Energy Resources Program.
Sources
Based on Assessment of Undiscovered Oil and Gas Resources in the Cuyo Basin Province, Argentina, 2017, by the Cuyo Basin Province Assessment Team, USGS Fact Sheet 2017–3042, U.S. Geological Survey; a work of the United States government in the public domain. The map and the split between shale and conventional resources are taken from the fact sheet's PDF, which the import had left out.
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