National and Global Petroleum Assessment

Assessment of Paleozoic Shale-Oil and Shale-Gas 

Resources in the Tarim Basin of China, 2018

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

of 1.4 billion barrels of shale oil and 26.9 trillion cubic feet of shale gas in Paleozoic formations in the Tarim Basin of China.

Introduction

The U.S. Geological Survey (USGS) quantitatively assessed 

the potential for unconventional (continuous) oil and gas resources 

within two Paleozoic organic-rich shales in the Tarim Basin of China 

(figs. 1 and 2): Lower Cambrian Yuertusi Formation and shales in the 

Middle Ordovician Series. These strata are the principal source rocks 

for conventional oil and gas fields in the interior of the Tarim Basin 

(Li and others 2018; Zhu, Chen, and others, 2018).

The Tarim Basin, the largest petroleum basin in China, encompasses 

563,000 square kilometers (km), and its Phanerozoic strata are as much 

as 16 km thick (Qiu and others, 2012). Although numerous oil and gas 

fields have been developed along its northern margin and in several 

uplifts in the basin’s interior, large parts of this remote basin remain 

unexplored. The USGS previously assessed the Tarim Basin’s conventional oil and gas resources (Charpentier and others, 2012). Paleozoic 

marine formations are currently preserved at depth and locally exposed 

around the basin’s periphery. They were deposited on the passive 

margin of the Tarim craton, a continental fragment proximal to the 

Gondwana margin. Since the late Paleozoic assembly of Central Asia, 

the Tarim Basin has been a vast nonmarine basin bounded on the south 

by the Tibetan Plateau and on the north by the Tien Shan. From the 

Carboniferous to the present, the basin’s margins have been strongly 

influenced by contractional deformation, including the ongoing Himalayan 

orogeny. This tectonic history has resulted in a relatively cool geothermal 

setting throughout the basin’s history; the current geothermal gradient 

is in the range of 20–23 degrees Celsius per km (Zhang, Huang, and 

others, 2015).

Geologic Background

The basal Cambrian Yuertusi Formation and the Middle Ordovician 

deep-marine section (Heituao and Shaergan Formations, for example) 

include organic-rich black shales with Type II kerogen (Qiu and others, 

2012) that represent maximum flooding surfaces in transgressive 

systems tracts both on the continental slope and in platform sags 

(Gao and others, 2007). The present total organic carbon (TOC) content 

of the Cambrian Yuertusi is 7–14 weight percent in outcrops north of the 

basin, whereas the Middle Ordovician source rocks have TOC contents 

of 0.5–2.9 weight percent. The Yuertusi is preserved at depth in the central 

and eastern part of the basin and is as much as 100 meters (m) thick 

(Zhu, Chen, and others, 2018). The Middle Ordovician source rocks are 

similarly distributed with thicknesses of as much as 100 m (Gao and 

others, 2007). Thermal maturities (Ro equivalent) of the Yuertusi exceed 

4 percent through much of the central part of the basin; Ro equivalent 

values are considerably lower (1–1.5 percent) at the top of the Middle 

Ordovician in the central part of the basin (Zhang, Liang, and others, 2007; 

Zhang, Huang, and others, 2015; Zhu, Huang, and others, 2015). Burialhistory models indicate that the Yuertusi was buried to depths sufficient 

to generate oil by the Ordovician or Silurian Periods (depending on location 

in the basin) and then oil was cracked to gas in the Mesozoic or Paleogene 

(Zhang, Huang, and others, 2015; Zhu, Huang, and others, 2015). Late 

Paleozoic and Mesozoic uplift raised the Ordovician section (in parts of 

the basin) into the oil-generation window where it has remained through 

the present day. Oil is preserved in the Ordovician section to depths 

of at least 7–8 km in the present Tarim Basin (Zhang, Huang, and 

others, 2015; Ma and others, 2017).

Deformed northern margin of the Tarim Basin and southern foothills of the Tien Shan, China.

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2019–3011

May 2019
Assessment Units

We defined three assessment units (AUs) (figs. 1 and 2): Lower 

Cambrian Yuertusi Shale Gas AU, Ordovician Shale Oil AU, and Ordovician 

Shale Gas AU. The AUs include only those areas where the organic-rich 

shale has sufficient thickness (greater than 15 m, the minimum net thickness permitted in USGS screening of international shale-gas and shale-oil 

resources) (Charpentier and Cook, 2011). In addition, areas where the 

potential shale reservoirs are deeper than 10 km are excluded, acknowledging 

the challenges of hydraulically stimulating wells at those depths. The 

margins of the basin are excluded from these AUs because they are strongly 

affected by fold/thrust belts and other faults, greatly increasing the leakage 

risk and disrupting the continuity of the reservoirs. The Ordovician Shale 

Oil AU includes those areas where the Middle Ordovician section is less 

than about 8 km deep, and the Ordovician Shale Gas AU includes those 

areas where the Middle Ordovician section is about 8–10 km deep. 

The geologic model for the Lower Cambrian Yuertusi Shale Gas 

AU incorporates oil generation from the organic-rich shale during early to 

middle Paleozoic voluminous continental-margin sedimentation, followed 

by preservation of the oil in the source rock through several periods of 

uplift in the late Paleozoic and Mesozoic Eras, and subsequent cracking 

of oil to gas during the Mesozoic to early Cenozoic. The presence of 

Yuertusi-sourced hydrocarbons in shallower conventional accumulations 

indicates that large volumes of hydrocarbons must have migrated out of the 

source rock during the basin’s evolution, whereas retention of a shale-gas 

resource in this AU would require that parts of the shale reservoir were 

relatively undisturbed by fractures and faults (migration pathways) during 

the Paleogene to present Himalayan orogeny. Recently, commercial 

quantities of gas attributed to a Yuertusi source were discovered in a 

conventional field at 6.9-km depth, higher within the Lower Cambrian 

Series (Zhu, Huang, and others, 2015; Zhu, Chen, and others, 2018). 

The geologic model for the Ordovician Shale Oil AU includes oil 

generation from organic-rich shale possibly beginning in the Permian 

but principally occurring in Paleogene time because burial of this unit 

was interrupted by several periods of uplift in the Paleozoic and Mesozoic

Eras. Oil is preserved in the shale source rock at depths as much as 8 km,

below which it has likely cracked to gas. The Ordovician Shale Gas 

AU encompasses the volume of rock in which the oil has cracked to 

gas, between 8 and 10 km deep. Success of these Ordovician AUs also 

depends on the presence of relatively unfractured volumes of self-sourced

shale reservoir. 

No Paleozoic shale-gas or shale-oil resources have been produced 

from the Tarim Basin, and we have assigned an AU-level probability of 

0.9 to all these AUs (table 1), meaning there is a 10-percent chance that 

there are no accumulations of the minimum size. 

Continuous oil and gas accumulations in the United States were 

used as analogs in these assessments. Table 1 lists the principal input 

data used for the assessments. 

Undiscovered Resources Summary

The USGS quantitatively assessed shale-oil and shale-gas resources

in Paleozoic strata of the Tarim Basin in China. The estimated mean total

for continuous oil resources is 1,373 million barrels of oil (MMBO), or

1.4 billion barrels of oil, with an F95–F5 range from 0 to 3,918 MMBO.

The mean total for continuous gas resources is 26,925 billion cubic feet 

(BCFG), or 26.9 trillion cubic feet, with an F95–F5 range from 

0 to 71,946 BCFG. The mean total for natural gas liquids is 128 million

barrels of natural gas liquids (MMBNGL) with an F95–F5 range from 

0 to 361 MMBNGL. These estimates are for undiscovered, technically 

recoverable resources of oil, gas, and natural gas liquids and do not 

reflect economically recoverable resources.

CHINA

KYRGYZSTAN

TAJIKISTAN

KAZAKHSTAN

PAKISTAN

INDIA

Ürümqi

Kashgar

AFGHANISTAN

T i e n S h a n

Qing Zang Gaoyuan

(Tibetan Plateau)

74° E 76° E 78° E 80° E 82° E 84° E 86° E 88° E 90° E 92° E 94° E

42° N

40° N

38° N

36° N

34° N

44° N

CHN

IND PAK

AFG

MNG KAZ

KGZ

TJK

UZB

Map

area

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

0 200 KILOMETERS 100

0 100 200 MILES EXPLANATION

Lower Cambrian Yuertusi Shale Gas AU

Tarim Basin boundary

Figure 1. Map showing location of the Tarim Basin, China, and the location of the Lower Cambrian Yuertusi Shale Gas Assessment Unit (AU).
References Cited

Charpentier, R.R., and Cook, T.A., 2011, USGS methodology for 

assessing continuous petroleum resources: U.S. Geological Survey Open-File Report 2011–1167, 73 p., accessed May 13, 2014, at 

https://pubs.usgs.gov/of/2011/1167/OF11-1167.pdf.

Charpentier, R.R., Schenk, C.J., Brownfield, M.E., Cook, T.A., 

Klett, T.R., Pitman, J.K., and Pollastro, R.M., 2012, Assessment of undiscovered conventional oil and gas resources of six 

geologic provinces of China: U.S. Geological Survey Fact Sheet 

2012–3117, 4 p.

Gao ZhiYong, Zhang ShuiChang, Zhang XingYang, and Zhu RuKai, 

2007, Relations between spatial distribution and sequence types 

of the Cambrian-Ordovician marine source rocks in Tarim Basin: 

Chinese Science Bulletin, v. 52, supp. 1, p. 92–102.

Li Yun, Xiong Yongqiang, Liang Qianyong, Fang Chenchen, 

Chen Yuan, Wang Xiaotao, Liao Zewen, and Peng Ping’an, 

2018, The application of diamondoid indices in the Tarim 

oils: American Association of Petroleum Geologists Bulletin, 

v. 102, no. 2, p. 267–291. [Also available at https://doi.org/

10.1306/0424171518217073.]

Ma Anlai, Jin Zhijum, Zhu Cuishan, and Bai Zhenrui, 2017, Cracking and thermal maturity of Ordovician oils from Tahe Oilfield, 

Tarim Basin, NW [northwest] China: Journal of Natural Gas 

Geoscience, v. 2, no. 4, p. 239–252. [Also available at https://

doi.org/10.1016/j.jnggs.2017.12.001.]

Qiu Nansheng, Chang Jian, Zuo Yinhui, Wang Jiyang, and Li Huili, 

2012, Thermal evolution and maturation of lower Paleozoic source 

rocks in the Tarim Basin, northwest China: American Association of 

Petroleum Geologists Bulletin, v. 96, no. 5, p. 789–821 [Also available at https://doi.org/10.1306/09071111029.]

Zhang ShuiChang, Liang DiGang, Zhu GuangYou, Zhang XingYang, 

Zhang BaoMin, Chen JianPing, and Zhang Bin, 2007, Fundamental 

geological elements for the occurrence of Chinese marine oil and gas 

accumulations: Chinese Science Bulletin, v. 52, supp. 1, p. 28–43. 

[Also available at https://doi.org/10.1007/s11434-007-6020-x.]

Zhang Shuichang, Huang Haiping, Su Jin, and Liu Mei, 2015, 

Ultra-deep liquid hydrocarbon exploration potential in cratonic 

region of the Tarim Basin inferred from gas condensate genesis: 

Fuel, v. 160, p. 583–595. [Also available at https://doi.org/

10.1016/j.fuel.2015.08.023.]

Zhu Guangyou, Chen Feiran, Wang Meng, Zhang Zhiyao, Ren Rong, 

and Wu Lin, 2018, Discovery of the lower Cambrian high-quality 

source rocks and deep oil and gas exploration potential in the Tarim 

Basin, China: American Association of Petroleum Geologists Bulletin, v. 102, no. 10, p. 2123–2151. [Also available at https://

doi.org/10.1306/03141817183.]

Zhu Guangyou, Huang Haiping, and Wang Huitong, 2015, Geochemical 

significance of discovery in Cambrian reservoirs at Well ZS1 of the 

Tarim Basin, northwest China: Energy Fuels, v. 29, no. 2, 

p. 1332−1344. [Also available at https://doi.org/10.1021/ef502345n.]

T i e n S h a n

CHINA

KYRGYZSTAN

KAZAKHSTAN

PAKISTAN

INDIA

Ürümqi

Kashgar

TAJIKISTAN

AFGHANISTAN

Qing Zang Gaoyuan

(Tibetan Plateau)

74° E 76° E 78° E 80° E 82° E 84° E 86° E 88° E 90° E 92° E 94° E

42° N

40° N

38° N

36° N

34° N

44° N

CHN

IND PAK

AFG

KAZ MNG

KGZ

TJK

UZB

Map

area

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

0 100 200 KILOMETERS

0 100 200 MILES

Tarim Basin boundary

Ordovician Shale Oil AU

Ordovician Shale Gas AU

EXPLANATION

Figure 2. Map showing location of the Tarim Basin, China, and the location of the Ordovician Shale Oil and Ordovician Shale Gas 

Assessment Units (AUs).
ISSN 2327-6916 (print) ISSN 2327-6932 (online) https://doi.org/10.3133/fs20193011

Photograph by Karen Nyberg, an Expedition 36 crew member on board the International 

Space Station, of the Tien Shan mountain range, central Asia.

Google Earth image of the Tarim Basin, China, showing 

about 1,000 kilometers (east–west); base map data from 

Google, Landsat/Copernicus, 2019.

Table 1. Key input data for three continuous assessment units (AUs) in the Tarim Basin, China.

[%, percent; EUR, estimated ultimate recovery per well; MMBO, million barrels of oil; BCFG, billion cubic feet of gas. Well drainage area, success ratio, and EUR are defined 

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

Assessment input data—

Continuous AUs

Ordovician Shale Oil AU Ordovician Shale Gas AU

Minimum Mode Maximum Calculated mean Minimum Mode Maximum Calculated 

mean

Potential production area of 

AU (acres) 1,000 1,000,000 18,700,000 6,567,000 1,000 2,000,000 11,597,600 4,532,867

Average drainage area of 

wells (acres) 60 100 120 93.3 40 80 120 80

Success ratio (%) 10 50 90 50 10 50 90 50

Average EUR (MMBO, oil; 

BCFG, gas) 0.02 0.04 0.1 0.043 0.2 0.35 0.8 0.373

AU probability 0.9 0.9

Assessment input data—

Continuous AU

Lower Cambrian Yuertusi Shale Gas AU

Minimum Mode Maximum Calculated mean

Potential production area of 

AU (acres) 1,000 3,000,000 19,653,000 7,551,333

Average drainage area of 

wells (acres) 40 80 120 80

Success ratio (%) 10 50 90 50

Average EUR (BCFG ) 0.2 0.35 0.8 0.373

AU probability 0.9

Table 2. Results for three continuous assessment units (AUs) in the Tarim Basin, China.

[MMBO, million barrels of oil; 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 systems 

and assessment units (AUs)

AU

probability

Accumulation 

type

Total undiscovered resources

Oil (MMBO) Gas (BCFG) NGL (MMBNGL)

F95 F50 F5 Mean F95 F50 F5 Mean F95 F50 F5 Mean

Ordovician Total Petroleum System

Ordovician Shale Oil AU 0.9 Oil 0 1,032 3,918 1,373 0 650 2,978 959 0 15 77 24

Ordovician Shale Gas AU 0.9 Gas 0 7,916 25,653 9,743 0 31 106 39

Cambrian Total Petroleum System

Lower Cambrian Yuertusi Shale 

Gas AU 0.9 Gas 0 13,015 43,315 16,223 0 51 178 65

Total undiscovered continuous 

resources 0 1,032 3,918 1,373 0 21,581 71,946 26,925 0 97 361 128

Tarim Basin Assessment Team 

Christopher J. Potter, Christopher J. Schenk, 

Tracey J. Mercier, Marilyn E. Tennyson, Thomas M. 

Finn, Cheryl A. Woodall, Heidi M. Leathers-Miller, 

Kristen R. Marra, Phuong A. Le, Ronald M. Drake II, 

Michael E. Brownfield, and Janet K. Pitman

For More Information

Assessment results are also available at the USGS 

Energy Resources Program website at https://energy.usgs.gov.