National and Global Petroleum Assessment

Assessment of Continuous Gas Resources of the North Caspian 

Basin Province, Kazakhstan and Russia, 2018

Introduction

The U.S. Geological Survey (USGS) quantitatively 

assessed the potential for undiscovered, technically recoverable continuous (unconventional) gas resources in the North 

Caspian Basin Province of Kazakhstan and Russia (fig. 1). The 

North Caspian Basin Province contains 20 kilometers of mainly 

Paleozoic sediment, making it one of the deepest basins in the 

world. The tectonic evolution of the basin is not well constrained 

given the extreme depth and the sparseness of data from the deep 

central part of the basin (Nevolin and Fedorov, 1995; Brunet 

and others, 1999; Ulmishek, 2001; Volozh and others, 2003; 

Okere and Toothill, 2012). Initiation of rifting and subsidence in 

the North Caspian Basin may have been as early as the Neoproterozoic (Brunet and others, 1999), but most likely began in 

the Ordovician, and rifting and subsidence were related to the 

opening of the Uralian Ocean (Ulmishek, 2001). Renewed and 

continuous subsidence from the Late Devonian to Early Permian may have been because of back-arc extension (Brunet and 

others, 1999), which resulted in the deposition of hundreds of 

meters of organic-rich source rocks in basinal areas; shallowwater platform carbonates that rimmed the basin are of similar 

age (Cook and others, 1999). Collision of terranes along the 

southern margin of the North Caspian Basin during the Early 

Permian partially isolated the basin and resulted in the deposition of as much as 5 kilometers of evaporites that partially seal 

the underlying Late Devonian–Early Permian source rocks. The 

progressive closure of the Uralian Ocean from late Carboniferous to the Triassic formed the Ural fold belt and the adjacent 

foreland, which filled with several kilometers of orogenic clastic 

sediments. This pulse of deposition resulted in the maturation of 

Late Devonian–Early Permian subsalt source rocks by burying 

them into the oil-generation window and into the gas window in 

the deep central part of the basin.

Total Petroleum System and Assessment Unit

For potential continuous oil and gas resources, the USGS 

defined a Paleozoic Composite Total Petroleum System (TPS) 

and a Paleozoic Subsalt Continuous Gas Assessment Unit (AU) 

within this TPS. Although deep-water, organic-rich shales ranging from the Late Devonian to Early Permian are cited as the 

major source rocks in this province, there is limited geochemical 

data on which to base this composite petroleum system, as 

samples are restricted to the basin margins (Ulmishek, 2001). 

Based on limited data, the shales contain Type II kerogen, have 

total organic carbon values of as much as 8 weight percent, have 

hydrogen index values of as much as 400 milligrams of hydrocarbon per gram of organic carbon, and are as much as several 

hundred meters thick (Pairazian, 1999; Ulmishek, 2001; Barde 

and others, 2002). In the central part of the basin, these shales 

are within the gas-generation window at depths greater than 

about 7,000 meters (Ulmishek, 2001).

The geologic model for the Paleozoic Composite TPS is for 

oil, generated from Late Devonian–Early Permian source rocks 

because of Permian–Triassic foredeep burial, to have cracked to 

gas with continued subsidence in the deep, overpressured central 

part of the basin. Gas from these source rocks migrated locally 

into, and was partially retained within, low permeability sandstones and shales, forming a regional, pervasive, continuous gas 

Figure 1. Map showing one continuous gas assessment unit (AU) 

in the North Caspian Basin Province of Kazakhstan and Russia. 

Province boundary is from Klett and others, 1997.

CASPIAN

SEA

ARAL

SEA

RUSSIA

KAZAKHSTAN

UZBEKISTAN

GEORGIA

45° E 50° E 55° E 60° E

50° N

45° N

0 100 200 KILOMETERS

0 100 200 MILES

North Caspian Basin Province

Paleozoic Subsalt Continuous Gas AU

EXPLANATION

Base map from U.S. Department of the Interior National Park Service

KAZ

TKM

UKR

UZB

GEO

Map

area

RUS

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2018–3051

September 2018

Using a geology-based assessment methodology, the U.S. Geological Survey estimated undiscovered, technically recoverable 

mean resources of 84.5 trillion cubic feet of continuous gas in the North Caspian Basin Province of Kazakhstan and Russia.
North Caspian Basin Province Assessment Team

Christopher J. Schenk, Tracey J. Mercier, Thomas M. Finn, Marilyn E. Tennyson, Phuong A. Le, Michael E. Brownfield, 

Kristen R. Marra, Stephanie B. Gaswirth, Heidi M. Leathers-Miller, and Ronald M. Drake II

For More Information

Assessment results are also available at the USGS Energy Resources Program website at https://energy.usgs.gov.

Table 1. Key input data for one continuous assessment unit (AU) in the North Caspian Basin Province 

of Kazakhstan and Russia.

[AU, assessment unit; %, percent; EUR, estimated ultimate recovery per well; BCFG, billion cubic feet of gas. Well 

drainage area, success ratio, and EUR are defined partly using U.S. shale-gas analogs. Shading indicates not applicable]

Assessment input data—Continuous AUs Paleozoic Subsalt Continuous Gas AU

Minimum Mode Maximum Calculated mean

Potential production area of AU (acres) 400 30,341,000 60,682,000 30,341,133

Average drainage area of wells (acres) 40 100 160 100

Success ratio (%) 10 50 90 50

Average EUR (BCFG) 0.1 0.5 1.5 0.55

AU probability 1.0

Table 2. Results for one continuous assessment unit (AU) in the North Caspian Basin Province of Kazakhstan and Russia.

[BCFG, billion cubic feet of gas; NGL, natural gas liquids; MMBNGL, million barrels of natural gas liquids. Results shown are fully risked estimates. F95 represents 

a 95-percent chance of at least the amount tabulated; other fractiles are defined similarly. Fractiles are additive under the assumption of perfect positive correlation. 

Shading indicates not applicable]

Total petroleum system and

assessment unit (AU)

AU

probability

Accumulation 

type

Total undiscovered resources

Gas (BCFG) NGL (MMBNGL)

F95 F50 F5 Mean F95 F50 F5 Mean

Paleozoic Composite Total Petroleum System

Paleozoic Subsalt Continuous Gas AU 1.0 Gas 17,797 71,488 196,412 84,543 67 278 819 338

Total undiscovered continuous resources 17,797 71,488 196,412 84,543 67 278 819 338

accumulation in the deep central part of the North Caspian Basin 

(Ulmishek, 2001). Uncertainty in the assessment is related to the 

degree of retention of gas within the subsalt section following 

generation and migration.

Assessment input data are summarized in table 1. Input 

data for drainage areas, success ratios, and estimated ultimate 

recoveries are taken from geologic analogs in the United States.

Undiscovered Resources Summary

The USGS quantitatively assessed continuous gas 

resources in one assessment unit (table 2) in the North Caspian 

Basin Province of Kazakhstan and Russia. For undiscovered, 

technically recoverable continuous gas resources, the mean 

totals are 84,543 billion cubic feet of gas (BCFG), or 

84.5 trillion cubic feet of gas, with an F95–F5 fractile range 

from 17,797 to 196,412 BCFG, and 338 million barrels of 

natural gas liquids (MMBNGL) with an F95–F5 fractile range 

from 67 to 819 MMBNGL.

References Cited

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at the eastern edge of the Precaspian basin—Impact of data integration 

on Upper Permian and Triassic prospectivity: American Association 

of Petroleum Geologists Bulletin, v. 86, no. 3, p. 399–415.

Brunet, M.F., Volozh, Y.A., Antipov, M.P., and Lobkovsky, L.I., 1999, 

The geodynamic evolution of the Precaspian Basin (Kazakhstan) 

along a north–south section: Tectonophysics, v. 313, nos. 1–2, 

p. 85–106.

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passive-margin carbonate platform of southern Kazakhstan—

Summary of depositional and stratigraphic models to assist in the 

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in the Precaspian petroliferous province: Journal of Petroleum 

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Okere, D., and Toothill, S., 2012, New insights into hydrocarbon plays in 

the Caspian Sea, Kazakhstan: Petroleum Geoscience, v. 18, p. 253–268.

Pairazian, V.V., 1999, A review of the petroleum geochemistry of the 

Precaspian Basin: Petroleum Geoscience, v. 5, p. 361–369.

Ulmishek, G.F., 2001, Petroleum geology and resources of the North 

Caspian Basin, Kazakhstan and Russia: U.S. Geological Survey 

Bulletin 2201–B, 25 p.

Volozh, Y., Talbot, C., and Ismail-Zadeh, A., 2003, Salt structures and 

hydrocarbons in the Pricaspian Basin: American Association of 

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ISSN 2327-6916 (print) ISSN 2327-6932 (online) https://doi.org/10.3133/fs2013051