A U.S. Geological Survey assessment from 2017, published as Fact Sheet 2017–3085 in February 2018.
Using a method built on the geology of the rocks, the U.S. Geological Survey (USGS) estimates that the Domanik-type formations of the Volga-Ural Region Province, in Russia, hold a mean of 2.8 billion barrels of undiscovered, technically recoverable continuous oil and 34 trillion cubic feet of gas.
What was assessed
The study looked at oil and gas that could be produced from the source rocks themselves — continuous, or unconventional, resources — in the Upper Devonian to Lower Carboniferous (Tournaisian) Domanik-type formations. These are the Domanik Formation and the Domanikoids, the younger rocks lying on top of it.
For this assessment, the USGS counted as a continuous oil and gas system rock that:
- contains at least 2 weight percent total organic carbon;
- lies within the thermal maturity window for generating oil or natural gas;
- has organic-rich shale at least 15 metres thick;
- contains Type I or Type II organic matter.
Many published studies cover these formations: their qualities as source rocks, their tectonic and thermal history, and when they matured and generated oil and gas. Several conventional oil fields, and some gas fields, have been found in the Volga-Ural region, producing from reservoirs usually in structural traps and reefs. No reports were available on how many wells produce directly from the Domanik-type formations rather than from conventional accumulations.
Figure 1. The three assessment units in the Volga-Ural Region Province. Base map from the National Park Service. USGS.
Three assessment units
The USGS defined the Domanik Total Petroleum System and three assessment units within it:
| Assessment unit | Where and what |
|---|---|
| Domanik Formation Continuous Oil | much of the province's eastern part. The Domanik source rock was laid down during a peak rise in sea level in the Late Devonian (early Frasnian), on top of older nearshore sediments |
| Domanikoid Continuous Oil | younger rocks deposited above the Domanik Formation in long troughs between reefs and carbonate platforms |
| Domanik Formation Foredeep Continuous Gas | the eastern part of the region, in a foredeep basin along the Ural Mountains, where the Domanik lies deeper and is presumed mature enough to generate gas |
Both oil units are thermally mature for oil generation.
The geology
Continuous oil production has been reported from the fractured Domanik Formation in the southern part of the basin. The Domanik is a self-sourced, organic-rich mudstone, with total organic carbon of at least 2 weight percent and mostly Type II kerogen, and it is mature for oil. Undiscovered continuous oil most likely lies between structural highs. The oil unit leaves out the areas of conventional fields and accumulations already discovered.
No continuous gas production has been reported from either oil unit. The foredeep unit is mature enough for gas, but few gas fields have been found there. Here too, undiscovered continuous gas most likely lies between structural highs, and the unit leaves out conventional fields already found on structural highs.
How the numbers were estimated
Detailed production data for continuous resources outside the United States are hard to get, so the method borrows from continuous oil and gas accumulations in the United States as analogues: the average amount each well ultimately recovers, the average area a well drains, and the range of well success ratios.
| Key input (minimum / mode / maximum / mean) | Domanik oil | Domanikoid oil | Foredeep gas |
|---|---|---|---|
| Potential production area (acres) | 1,000 / 15,936,500 / 31,873,000 / 15,936,833 | 1,000 / 7,484,000 / 14,967,000 / 7,484,000 | 1,000 / 14,755,000 / 29,510,000 / 14,755,333 |
| Average drainage area of a well (acres) | 120 / 180 / 240 / 180 | 120 / 180 / 240 / 180 | 80 / 120 / 160 / 120 |
| Success ratio (percent) | 10 / 30 / 70 / 36.7 | 10 / 25 / 60 / 31.7 | 10 / 50 / 90 / 50 |
| Average estimated ultimate recovery per well | 0.03 / 0.06 / 0.15 / 0.065 million barrels | 0.02 / 0.05 / 0.1 / 0.052 million barrels | 0.2 / 0.5 / 1.0 / 0.522 billion cubic feet |
Results
The estimated means are:
- oil: 2,787 million barrels, with an F95–F5 range from 663 to 6,072 million barrels;
- natural gas: 33,558 billion cubic feet, from 7,823 to 71,455 billion cubic feet;
- natural gas liquids: 1,343 million barrels, from 308 to 2,884 million barrels.
| Assessment unit | Oil, million barrels (F95 / F50 / F5 / mean) | Gas, billion cubic feet | Natural gas liquids, million barrels |
|---|---|---|---|
| Domanik oil | 494 / 1,831 / 4,599 / 2,098 | 236 / 899 / 2,364 / 1,049 | 9 / 35 / 98 / 42 |
| Domanikoid oil | 169 / 612 / 1,473 / 689 | 81 / 300 / 757 / 344 | 3 / 12 / 32 / 14 |
| Foredeep gas | — | 7,506 / 28,875 / 68,334 / 32,165 | 296 / 1,145 / 2,754 / 1,287 |
| Total | 663 / 2,443 / 6,072 / 2,787 | 7,823 / 30,074 / 71,455 / 33,558 | 308 / 1,192 / 2,884 / 1,343 |
F95 means a 95 percent chance of at least the amount shown, and the other columns are read the same way. The results are fully risked; for gas accumulations, all liquids are counted as natural gas liquids.
Sources
- Klett, T.R., Brownfield, M.E., Finn, T.M., Gaswirth, S.B., Le, P.A., Leathers-Miller, H.M., Marra, K.R., Mercier, T.J., Pitman, J.K., Schenk, C.J., Tennyson, M.E., and Woodall, C.A., Assessment of Undiscovered Continuous Oil and Gas Resources in the Domanik-Type Formations of the Volga-Ural Region Province, Russia, 2017, U.S. Geological Survey Fact Sheet 2017–3085, February 2018. https://doi.org/10.3133/fs20173085 — the map, the input table and the results recovered from the PDF, which the imported page had lost.
- The fact sheet draws on Charpentier and Cook (2011), Fadeeva and others (2016), Peterson and Clarke (1983), Ulmishek (1988) and Zaydelson and others (1991).
- Rewritten in hubnx's own words.
Licence: CC0 1.0 (public domain) · Adapted from pubs.usgs.gov
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