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Using a method based on geology, the U.S. Geological Survey estimates that the Maracaibo Basin Province of Venezuela and Colombia holds, on average, 656 million barrels of oil and 5.7 trillion cubic feet of gas in undiscovered continuous (unconventional) accumulations that could be recovered with current technology.
The basin
The Maracaibo Basin Province is a structurally complex region of about 58,000 square kilometres between the Sierra de Perijá and the Cordillera de Mérida; its northern edge is usually placed at the Oca–Ancón fault. More than 30 billion barrels of conventional oil have come out of it, ranking it among the world's leading petroleum basins.
Its main source rock is the organic-rich shale of the Upper Cretaceous La Luna Formation, which is mature enough to have generated oil and gas across much of the basin. The study set out to estimate how much recoverable oil and gas is still held in the La Luna source rock after two phases of generation and expulsion, and to consider whether gas may sit in low-permeability ("tight") sandstones. Part of the La Luna is mapped in the gas window, but little is known about where gas may be, whether in the source rock or in deeply buried tight sandstones.
The Maracaibo Basin Province and its three continuous assessment units, around Lago de Maracaibo. USGS map, on a National Park Service base.
Three assessment units
The USGS defined a La Luna Continuous Total Petroleum System with three assessment units: La Luna Continuous Oil, La Luna Continuous Gas and Maracaibo Tight Gas. The main risk is whether recoverable oil and gas stayed in the source rock after migration. The geological model is that some of the oil and gas was retained in the La Luna, and that gas may have migrated into tight sandstones — though whether such sandstones exist at all is highly uncertain.
Well drainage areas, recovery per well and success rates were taken from U.S. shale-oil, shale-gas and tight-gas plays. The geological probability that a unit holds gas at all was put at 0.9 for the La Luna gas unit and 0.5 for the tight-gas unit.
The results
| Assessment unit | Oil, mean | Gas, mean | Gas range (F95–F5) |
|---|---|---|---|
| La Luna Continuous Oil | 656 million barrels (111 to 1,632) | 1,314 billion cubic feet | 208 to 3,389 |
| La Luna Continuous Gas | — | 2,923 billion cubic feet | 0 to 8,173 |
| Maracaibo Tight Gas | — | 1,476 billion cubic feet | 0 to 5,566 |
| Total | 656 million barrels | 5,713 billion cubic feet | 208 to 17,128 |
Natural gas liquids add a mean of 127 million barrels (8 to 362). The zeros at the low end for the gas units reflect the chance that they hold no gas at all.
Sources
- Maracaibo Basin Province Assessment Team (Christopher J. Schenk, Marilyn E. Tennyson, Tracey J. Mercier, Stephanie B. Gaswirth, Kristen R. Marra, Phuong A. Le, Janet K. Pitman, Michael E. Brownfield, Sarah J. Hawkins, Heidi M. Leathers-Miller, Thomas M. Finn and Timothy R. Klett), Assessment of Continuous Oil and Gas Resources of the Maracaibo Basin Province of Venezuela and Colombia, 2016, USGS Fact Sheet 2017–3011, March 2017. https://doi.org/10.3133/fs20173011
- Results: USGS Energy Resources Program, http://energy.usgs.gov
Licencia: CC0 1.0 (dominio público) · Adaptado de pubs.usgs.gov
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