National and Global Petroleum Assessment

Assessment of Undiscovered Continuous Gas Resources in the 

Amu Darya Basin Province of Turkmenistan, Uzbekistan, Iran, and 

Afghanistan, 2017

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

continuous resources of 35.1 trillion cubic feet of gas in the Amu Darya Basin Province of Turkmenistan, Uzbekistan, Iran, and Afghanistan.

Introduction

The U.S. Geological Survey (USGS) completed an assessment of undiscovered, technically recoverable continuous 

(unconventional) gas resources in the Amu Darya Basin Province 

of Turkmenistan, Uzbekistan, Iran, and Afghanistan (fig. 1). 

The Amu Darya Basin is a mosaic of Early to Middle Jurassic 

horsts and grabens formed in an extensional back-arc realm as 

north-directed subduction and an associated volcanic arc formed 

during the Early Jurassic following the Late Triassic closure of 

the paleo-Tethys Ocean (Otto, 1997; Ulmishek, 2004; Smit and 

others, 2013; Brunet and others, 2014). Initially, the grabens 

were sites of thick successions of nonmarine clastics, coals, 

and carbonaceous shales. As extension decreased and thermal 

sag occurred after the Middle Jurassic, transgression led to a 

succession of Middle Jurassic marine sediments (Bathonian and 

Callovian), culminating in the development of extensive Upper 

Jurassic (Oxfordian) carbonate platforms on the horsts, and thick 

sequences of organic-rich shales in the deep grabens (Ulmishek, 

2004). In the Late Jurassic (Kimmeridgian–Tithonian), up 

to 900 meters of evaporites of the Gaurdak Formation were 

deposited, which covered and sealed the older rocks. Marine 

conditions were reestablished following transgression in the 

Early Cretaceous (Barremian), and marine back-arc conditions 

persisted until the Oligocene with up to 7 kilometers of sediment 

deposited in some grabens, such as the Murgab depression, in 

the central part of the basin. The collision of India with Eurasia 

and the closure of the neo-Tethys Ocean in the Oligocene led 

to a regional unconformity and minor uplift (Otto, 1997). The 

formation of the north-directed Kopet Dag fold belt along the 

southern margin of the Amu Darya Basin in the Neogene (Robert 

and others, 2014) resulted in a foredeep that further thermally 

matured Jurassic source rocks. Lower Jurassic coals and carbonaceous shales and Upper Jurassic calcareous, organic-rich shales 

are the principal petroleum source rocks in the basin (Ulmishek, 

2004) and are the basis for the definition of two total petroleum 

systems (TPSs).

Total Petroleum Systems and Assessment Units

In the Amu Darya Basin Province, the USGS defined an 

Oxfordian Shale TPS and an Oxfordian Shale Gas Assessment 

Unit (AU) within this TPS and a Lower–Middle Jurassic TPS 

and a Lower–Middle Jurassic Tight Gas AU within this TPS 

(fig. 1).

The Oxfordian shales are up to 250 meters thick and are 

described as black, organic-rich, and bituminous. Organic matter 

in the shales is oil-prone Type II and IIS with total organic carbon 

values up to 15 weight percent (Ulmishek, 2004). Gas in the Amu 

Darya Basin, presumably sourced by these shales, can contain up 

to 8 percent hydrogen sulfide. Oxfordian shales achieved thermal 

maturation for oil generation during the Late Cretaceous and for 

gas generation during the Neogene (Ulmishek, 2004). The geologic 

model for the Oxfordian Shale Gas AU is for oil to have been generated (and subsequently thermally cracked to gas) from organicrich Oxfordian marine shales in the deep, central part of the basin. 

Some portion of the gas was retained within the shales following 

migration to form potentially recoverable resources.

UZBEKISTAN

TURKMENISTAN

AFGHANISTAN

IRAN

KAZAKHSTAN

Mazār-e Sharīf

Mary

Amu Darya

58° 60° 62° 64° 66°

42°

40°

38°

36°

34°

Source: U.S. Department of the Interior National Park Service

Oxfordian Shale Gas AU

Amu Darya Basin Province boundary

EXPLANATION

Lower–Middle Jurassic Tight Gas AU

Murgab

depression

0 50 100 KILOMETERS

0 50 100 MILES

Türkmenabat

Kopet Dag fold belt

Map

area

IRN

IND

KAZ

CHN

PAK

AFG

SAU

TKM UZB KGZ RUS

AZE

TJK

IRQ KWT

Figure 1. Location of the Amu Darya Basin Province in Turkmenistan, 

Uzbekistan, Iran, and Afghanistan, and the two assessment units 

(AUs) defined in this study.

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2017–3058

August 2017
The geologic model for the Lower–Middle Jurassic Tight Gas 

AU is for gas generated from gas-prone Type III organic matter in 

coals and carbonaceous shales to have migrated locally into, and to 

have been trapped within, low-permeability, nonmarine sandstones 

and siltstones. This tight gas AU may span a stratigraphic interval 

up to 1,600 meters thick and is greater than 5 kilometers deep. 

This model predicts the presence of a regional tight-gas system in 

these rocks primarily within the central part of the basin.

Assessment input data for the two AUs are shown in table 1.

Undiscovered Resources Summary

The USGS quantitatively assessed undiscovered continuous shale-gas and tight-gas resources in the Amu Darya 

Basin Province (table 2). For undiscovered gas resources, 

the estimated mean totals are 35,105 billion cubic feet 

of gas (BCFG), or 35.1 trillion cubic feet of gas, with an 

F95–F5 range from 4,879 to 103,529 BCFG and 235 million barrels of natural gas liquids (MMBNGL) with an 

F95–F5 range from 37 to 658 MMBNGL. For the Oxfordian 

Shale Gas AU, the estimated mean is 21,278 BCFG with an 

F95–F5 range from 4,879 to 45,856 BCFG and 170 MMBNGL 

with an F95–F5 range from 37 to 381 MMBNGL. For 

the Lower–Middle Jurassic Tight Gas AU, the estimated 

mean is 13,827 BCFG with an F95–F5 range from 0 to 

57,673 BCFG and 65 MMBNGL with an F95–F5 range from 

0 to 277 MMBNGL. The range of resource estimates reflects 

the geologic uncertainty on this relatively underexplored, deep 

central part of the Amu Darya Basin Province.

Table 1. Key assessment input data for two continuous assessment units in the Amu Darya Basin Province of Turkmenistan, Uzbekistan, 

Iran, and Afghanistan.

[AU, assessment unit; %, percent; EUR, estimated ultimate recovery per well; BCFG, billion cubic feet of gas. Well drainage area, success ratio, and EUR are from 

U.S. shale-gas and tight-gas analogs. The average EUR input is the minimum, median, maximum, and calculated mean. Shading indicates not applicable]

Assessment input data—

Continuous AUs

Oxfordian Shale Gas AU Lower–Middle Jurassic Tight Gas AU

Minimum Mode Maximum Calculated mean Minimum Mode Maximum Calculated mean

Potential production area of AU (acres) 800 9,695,000 19,390,000 9,695,267 400 3,300,200 33,002,000 12,100,867

Average drainage area of wells (acres) 80 120 160 120 40 120 210 120

Success ratios (%) 10 50 90 50 10 50 90 50

Average EUR (BCFG) 0.2 0.5 1.1 0.528 0.2 0.5 1.1 0.528

AU probability 1.0 0.5

Table 2. Assessment results for two continuous assessment units in the Amu Darya Basin Provincen of Turkmenistan, Uzbekistan, Iran, and 

Afghanistan.

[BCFG, billion cubic feet of gas; NGL, natural gas liquids; MMBNGL, million barrels of natural gas liquids. Results shown are fully risked estimates. For gas accumulations, all liquids are included in the NGL category. 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 systems and

assessment units (AUs)

AU

probability

Accumulation

type

Total undiscovered resources

Gas (BCFG) NGL (MMBNGL)

F95 F50 F5 Mean F95 F50 F5 Mean

Oxfordian Shale Total Petroleum System

Oxfordian Shale Gas AU 1.0 Gas 4,879 18,914 45,856 21,278 37 147 381 170

Lower–Middle Jurassic Total Petroleum System

Lower–Middle Jurassic Tight Gas AU 0.5 Gas 0 0 57,673 13,827 0 0 277 65

Total undiscovered continuous resources 4,879 18,914 103,529 35,105 37 147 658 235

References Cited

Brunet, M.-F.; Ershov, Andrey; Korotaev, Maxim; Mordvintsev, Dmitriy; Barrier, Eric; and Sidorova, Irina, 2014, Mesozoic evolution of the Amu Darya basin [abs.]: 

EGU General Assembly 2014, April 27–May 2, 2014, Vienna, Austria, Proceedings, Geophysical Research Abstracts, v. 16, EGU2014–10882, 1 p.

Otto, S.C., 1997, Mesozoic-Cenozoic history of deformation and petroleum systems in sedimentary basins of Central Asia—Implications of collisions on the Eurasian 

margin: Petroleum Geoscience, v. 3, no. 4, p. 327–341.

Robert, A.M.M.; Letouzey, Jean; Kavoosi, M.A.; Sherkati, Sharham; Müller, Carla; Vergés, Jaume; and Aghababaei, Abdollah, 2014, Structural evolution of the 

Kopeh Dagh fold-and-thrust belt (NE Iran) and interactions with the South Caspian Sea Basin and Amu Darya Basin: Marine and Petroleum Geology, v. 57, 

p. 68–87.

Smit, J.H.W.; Cloetingh, S.A.P.L.; Burov, E.B.; Tesauro, Magdala; Sokoutis, Dimitrios; and Kaban, M.K., 2013, Interference of lithospheric folding in western Central 

Asia by simultaneous Indian and Arabian plate indentation: Tectonophysics, v. 602, p. 176–193.

Ulmishek, G.F., 2004, Petroleum geology and resources of the Amu-Darya Basin, Turkmenistan, Uzbekistan, Afghanistan, and Iran: U.S. Geological Survey 

Bulletin 2201–H, 32 p.

For More Information

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

Amu Darya Basin Province Assessment Team

Christopher J. Schenk, Marilyn E. Tennyson, Tracey J. Mercier, Sarah J. Hawkins, Stephanie B. Gaswirth, Kristen R. Marra, 

Timothy R. Klett, Phuong A. Le, Michael E. Brownfield, and Cheryl A. Woodall

ISSN 2327-6916 (print) ISSN 2327-6932 (online) https://doi.org/10.3133/fs20173058