Introduction

The U.S. Geological Survey (USGS) quantitatively assessed the potential for undiscovered, technically recoverable conventional oil and gas resources in eight geologic provinces in the Greater Caspian area (fig. 1). This assessment encompasses North Caspian Basin, North Ustyurt Basin, Middle Caspian Basin, Azov-Kuban Basin, South Caspian Basin, Kura Basin, Dnieper-Donets Basin, and Pripyat Basin Provinces.

The petroleum systems of the Greater Caspian area reflect the complex tectonic evolution of the continental margin of northeast Pangaea that bordered the Paleotethys and Neotethys Oceans (Otto, 1997; Brunet and others, 2003; Golonka, 2007). The basins assessed in this study are largely polyphase in that their modern structural configurations are the result of several tectonic processes. Accommodation space in these provinces is formed by subsidence in regional rifts, back-arc basins, intra-arc basins, thermal sag basins, and foreland basins, or combinations of these structural elements (Otto, 1997; Golonka, 2007; Boote and others, 2018).

Total Petroleum Systems and Assessment Units

In the Greater Caspian area, the USGS defined a Paleozoic–Mesozoic Composite Total Petroleum System (TPS) in the North Caspian Basin Province; Paleozoic Composite TPS in the North Ustyurt Basin Province; Mesozoic Composite TPS in the North Ustyurt Basin Province; Mesozoic–Cenozoic Composite TPS in the Middle Caspian Basin Province; Mesozoic–Cenozoic Composite TPS in the Azov-Kuban Basin Province; Mesozoic–Cenozoic Composite TPS in the South Caspian Basin Province; Mesozoic–Cenozoic Composite TPS in the Kura Basin Province; Paleozoic Composite TPS in the Dnieper-Donets Basin Province; and Paleozoic Composite TPS in the Pripyat Basin Province. The TPS names reflect the major source rock ages. Paleozoic source rocks are present in the Dnieper-Donets Basin, Pripyat Basin, North Caspian Basin, and North Ustyurt Basin Provinces. Paleozoic petroleum source rocks are organic-rich marls in carbonate intraplatform basins, Devonian synrift and postrift organic-rich marine shales, Carboniferous marine shales and marls and coals, and carbonaceous shales (Ulmishek, 2001b; Okere and Toothill, 2012). Mesozoic and Cenozoic source rocks are present in the North Ustyurt Basin, Middle Caspian Basin, Azov-Kuban Basin, South Caspian Basin, and Kura Basin Provinces (Otto, 1997; Ulmishek, 2001a, 2001c; Okere and Toothill, 2012). Mesozoic source rocks are Jurassic and Cretaceous carbonate intraplatform organic-rich marls and Jurassic lacustrine shale, coal beds, and carbonaceous shale. Cenozoic source rocks are dominated by Oligocene to Miocene Maykop Formation organic-rich marine shales and possibly diatomites (Smith-Rouch, 2006; Sachsenhofer and others, 2018, 2021). Fifteen assessment units (AUs) were defined within the TPSs, and each AU was assessed for undiscovered conventional oil and gas resources. Key assessment input data are summarized in table 1 and in Schenk (2025).

Undiscovered Resources Summary

The USGS quantitatively assessed undiscovered conventional oil, gas, and natural gas liquids resources within 15 AUs in the Greater Caspian area (table 2). The fully risked mean totals are 34,335 million barrels of oil (MMBO) or 34.3 billion barrels of oil, with an F95–F5 fractile range from 13,519 to 67,172 MMBO; 319,574 billion cubic feet of gas (BCFG), or 320 trillion cubic feet, with an F95–F5 range from 122,871 to 626,967 BCFG; and 7,421 million barrels of natural gas liquids (MMBNGL), or 7.4 billion barrels of natural gas liquids, with an F95–F5 range from 2,858 to 14,628 MMBNGL.

For More Information

Assessment results are also available at the USGS Energy Resources Program website, https://www.usgs.gov/programs/energy-resources-program.

Greater Caspian Assessment Team

Christopher J. Schenk, Tracey J. Mercier, Phuong A. Le, Andrea D. Cicero, Ronald M. Drake II, Thomas M. Finn, Sarah E. Gelman, Jane S. Hearon, Benjamin G. Johnson, Jenny H. Lagesse, Heidi M. Leathers-Miller, and Kira K. Timm