Undiscovered Oil and Gas in the Amu Darya and Afghan-Tajik Basins: A USGS Estimate

The U.S. Geological Survey has estimated how much undiscovered, technically recoverable conventional oil and gas lies in the Amu Darya Basin and Afghan-Tajik Basin provinces, which span Turkmenistan, Uzbekistan, Tajikistan, Afghanistan and Iran.

The two conventional oil and gas assessment units. U.S. Geological Survey

The estimate

F95 means a 95% chance of at least that amount; F5, a 5% chance. The estimates are fully risked.

By assessment unit:

The assessors' calculated means were 717.1 undiscovered gas fields and 76.8 oil fields in the Amu Darya unit, and 61.5 gas and 10.3 oil fields in the Afghan-Tajik unit. Median field sizes were 4 million barrels of oil and 24 billion cubic feet of gas in both; the largest gas field allowed for was 40,000 billion cubic feet in the Amu Darya unit and 2,000 in the Afghan-Tajik.

How the basins formed

The two basins were one geologic unit until the Pamir block collided in the Miocene and pushed up the thrusts, folds and anticlines that now separate them.

1. Latest Triassic to Early Jurassic: north-directed subduction and a volcanic arc; behind it, stretching formed horsts and grabens (Early to Middle Jurassic).
2. The grabens filled with thick nonmarine sandstones, mudstones, coal beds and carbonaceous shales.
3. As stretching slowed, the sea came in: Callovian to Oxfordian carbonate platforms, with organic-rich calcareous shales in the basins beside them.
4. Kimmeridgian to Tithonian: slight uplift restricted the sea, leaving up to 900 meters of salt and anhydrite — the Gaurdak Formation.
5. Early Cretaceous to Oligocene: repeated rises and falls of the sea laid down up to 7 kilometers of sandstone, mudstone and some carbonate in the deeper grabens.
6. Miocene: collision and contraction folded the rocks into the broad folds and anticlines that hold many of the oil and gas reservoirs. Extra burial may have matured Paleogene source rocks in the Afghan-Tajik Basin, while those in the Amu Darya Basin stayed immature.

Where the oil and gas come from, and collect

Source rocks, below the salt:

• Lower to Middle Jurassic coal beds, carbonaceous shales and lake shales — coal is the main gas source in the Amu Darya Basin, and the condensate has been interpreted as coming from coal too.
• Callovian to Oxfordian marine marls and shales — up to 15 weight-percent organic carbon, up to 250 meters thick, mainly type-IIS kerogen.

These are modelled to be mostly in the gas window across the Amu Darya Basin, except in a narrow zone along its edges. The Afghan-Tajik Basin may add Paleogene organic-rich marine shales, possibly matured in the Neogene.

Reservoirs:

• Below the salt: carbonate reefs, patch reefs, dolomites, karst, ooid shoals and carbonate debris flows, partly sealed by the Gaurdak salt. The deepest may be highly overpressured and naturally fractured.
• Above the salt: Cretaceous to Oligocene river, delta, near-shore, shelf and deep-water sandstones — above all the Lower Cretaceous Shatlyk Formation — charged where faults and gaps in the seal let hydrocarbons rise. Neogene folds hold most of the Amu Darya unit's resources.
• In the Afghan-Tajik Basin, similar carbonates and Paleogene sandstones; the Pamir collision may have re-routed or lost oil and gas from earlier traps.

More results: USGS Energy Resources Program.

Sources

Based on Assessment of Undiscovered Conventional Oil and Gas Resources in the Amu Darya Basin and Afghan-Tajik Basin Provinces of Turkmenistan, Uzbekistan, Tajikistan, Afghanistan, and Iran, U.S. Geological Survey Fact Sheet 2026–3024, by Christopher J. Schenk, Tracey J. Mercier, Phuong A. Le, Andrea D. Cicero, Sarah E. Gelman, Jane S. Hearon, Benjamin G. Johnson, Jenny H. Lagesse and Heidi M. Leathers-Miller, USGS Publications Warehouse; a work of the United States government in the public domain.