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As part of its National and Global Petroleum Assessment, the U.S. Geological Survey (USGS) used a geology-based method to estimate the undiscovered, technically recoverable conventional oil and gas in the West Siberian Basin Province of Russia — the world's largest basin by area and by known volumes of conventional oil and gas. The mean estimates are 12.9 billion barrels of oil and 684.3 trillion cubic feet of gas.
Decades of exploration have tested most of the structural traps on land and found many giant and supergiant oil and gas fields. The offshore is far less explored and is likely to be the focus of future work: many large undrilled structures beneath the southern Kara Sea are thought to hold major undiscovered gas. The assessment covers the whole province and also estimates what lies north of the Arctic Circle.
Figure 1. The three assessment units in the West Siberian Basin Province, modified from Schenk (2018). Base map from the U.S. Department of the Interior, National Park Service. Credit: U.S. Geological Survey.
Where the oil and gas came from
The USGS defined a single Mesozoic Composite Total Petroleum System, because in parts of the basin — especially the gas-rich north — oil and gas cannot be tied firmly to any one of several possible source rocks. Candidate sources include organic-rich parts of the Triassic Tampey Formation, the Lower to Middle Jurassic Tyumen Formation, the Lower Jurassic Togur Formation, the Upper Jurassic–Lower Cretaceous Bazhenov Formation, the Upper Jurassic Vasyugen Formation, and the shales and coals of the Cretaceous Pokur Formation.
Most of the basin's oil comes from the organic-rich marine shales of the Bazhenov Formation, with the Togur, Tyumen and Tampey shales as secondary sources. The Bazhenov becomes more thermally mature to the north, where it is buried as deep as 15 kilometers, and in the north all the potential source rocks — Bazhenov shales and Pokur and Tyumen coals among them — are most likely major sources of gas.
Three assessment units
The three units share a tectonic and depositional history since the Triassic.
- Southern West Siberian Basin Reservoirs. Oil and minor gas, mainly from the Bazhenov, migrated upward and updip into sandstones in structural traps associated with paleotopography on complexly structured, rifted basement; in stratigraphic traps in rifts; in Neocomian marine clinoforms; in basin-floor fans; and filling incised valleys. Most oil fields are in clinoform sandstones of the Lower Cretaceous Achimov Formation.
- Northern West Siberian Basin Reservoirs. Similar, but much of the oil was thermally cracked to gas, adding to gas generated mainly from coals. Gas moved into sandstones in structural and stratigraphic traps, possibly helped by late Cenozoic uplift and gas expansion. The biggest structures have probably been tested, but few stratigraphic traps have.
- South Kara Sea Offshore Reservoirs. Oil migrated into reactivated structural traps and stratigraphic traps and was then cracked to gas, in mainly Upper Jurassic to Upper Cretaceous sandstones like those to the south. Many large structures are untested.
Results
Fully risked mean estimates for the whole province:
| Assessment unit | Oil (million barrels) | Gas in oil accumulations (billion cubic feet) | Gas in gas accumulations (billion cubic feet) |
|---|---|---|---|
| Southern West Siberian Basin | 9,862 | 7,892 | 8,591 |
| Northern West Siberian Basin | 1,367 | 820 | 59,160 |
| South Kara Sea Offshore | 1,669 | 1,669 | 606,147 |
In total that is 12,898 million barrels of oil (F95–F5 range 7,616 to 21,004), 684,279 billion cubic feet of gas (292,363 to 1,237,301), and 5,400 million barrels of natural gas liquids (2,586 to 9,316). F95 means a 95 percent chance of at least that amount.
North of the Arctic Circle, the mean estimates are 2,731 million barrels of oil (899 to 6,308), 651,940 billion cubic feet of gas (271,409 to 1,190,550) and 4,690 million barrels of natural gas liquids (2,127 to 8,289).
Sources
Based on "Assessment of Undiscovered Conventional Oil and Gas Resources of the West Siberian Basin Province, Russia, 2020," U.S. Geological Survey Fact Sheet 2022–3047 (September 2022), published by the U.S. Geological Survey; rewritten in hubnx's own words.
- The map and the results by assessment unit come from the fact sheet's PDF: https://pubs.usgs.gov/fs/2022/3047/fs20223047.pdf
- Input data are in Schenk (2022), a USGS data release; the fact sheet also draws on Ulmishek (2003) and other studies of the basin's geology.
Licence : CC0 1.0 (domaine public) · Adapté de pubs.usgs.gov
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