U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2019–3010

April 2019

National and Global Petroleum Assessment

Assessment of Mesozoic Tight-Oil and Tight-Gas Resources 

in the Sichuan Basin of China, 2018

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

of 1.2 billion barrels of tight oil and 29.1 trillion cubic feet of tight gas in Mesozoic formations in the Sichuan Basin of China. 

Introduction

In 2018, the U.S. Geological Survey (USGS) quantitatively assessed the 

potential for unconventional (continuous) oil and gas resources in Mesozoic 

nonmarine clastic rocks in the Sichuan Basin of China (fig. 1) that include tight 

gas in the Upper Triassic Xujiahe Formation and tight oil in Lower Jurassic 

lacustrine strata of the Lianggaoshan Formation and the Da’anzhai Member of 

the Ziliujing Formation. Previous USGS oil and gas assessments in this basin 

include a 2015 shale-gas assessment in three Paleozoic stratigraphic intervals 

in the Sichuan Basin (Potter and others, 2015; Potter, 2018) and a 2012 

assessment of conventional oil and gas resources in six major Chinese basins 

(Charpentier and others, 2012).

Chinese national oil companies currently produce tight gas from the 

Xujiahe (Zhao, Bian, and others, 2013) and tight oil from the Da’anzhai and 

Lianggaoshan (Chen and others, 2015; Yang and others, 2016) in the central 

part of the Sichuan Basin. The Xujiahe is a thick fluvial unit that includes three 

widely distributed coaly gas-prone (Type III) source intervals, each generally 

50–150 meters (m) thick and containing numerous coal beds that are a few meters 

thick (Zou, Tao, and others, 2009; Zhu and others, 2012). These source intervals 

are alternately stacked with three low-permeability sand reservoir intervals 

(up to 40 m thick with individual sand reservoirs 3–8 m thick) (Zou, Tao, and 

others, 2009; Zhao, Bian, and others, 2013; Zou, Gong, and others, 2013). The 

Da’anzhai and Lianggaoshan contain lacustrine black shales that are rich in 

Type I and II (oil-prone) organic matter (Li and others, 2014) and are interbedded 

with tight reservoir units that include a shelly limestone (Da’anzhai) and a sandstone (Lianggaoshan) (Yang and others, 2016). The Da’anzhai is 0–60 m thick, 

and the Lianggaoshan is 0–100 m thick (Yang and others, 2016).

Assessment Units

We defined the Triassic Xujiahe Tight Gas Assessment Unit (AU) within 

the Triassic Total Petroleum System and the Lower Jurassic Tight Oil AU within 

the Jurassic Total Petroleum System. These AUs (fig. 1) are confined to parts of 

the Sichuan Basin’s relatively undeformed central uplift area in which sufficient 

thicknesses of these units are present in the subsurface.

The geologic model for the Triassic Xujiahe Tight Gas AU is predicated 

on burial of Xujiahe coal source rocks to depths of at least 4–5 kilometers during 

voluminous Mesozoic nonmarine sedimentation. Thermal maturation modeling 

indicates that these rocks began to generate gas in the Late Jurassic to Early 

Cretaceous (above wet gas threshold, thermal maturity [Ro

] of 0.6–1.0 percent) 

and achieved peak gas generation (1.0–1.3 percent Ro

) by the end of the Cretaceous 

(Zhao, Wang, and others, 2010; Qin and others, 2018). Short distance migration 

charged adjacent low-permeability sandstone bodies. The pressure coefficient in 

the gas reservoirs is 1.1–1.5, indicating strong overpressure (Zou, 2017).

The geologic model for the Lower Jurassic Tight Oil AU comprises generation of oil through Mesozoic burial of oil-prone organic-rich lacustrine shales in the 

Da’anzhai and Lianggaoshan and short-distance vertical migration into adjacent 

tight reservoirs. Lower Jurassic organic-rich shales are currently within (and 

slightly above) the oil window (0.9–1.5 percent Ro

) (Yang and others, 2016). 

Chen and others (2015) reported that oil was present in fractures, microfissures, 

and matrix porosity in the Da’anzhai. The Da’anzhai and Lianggaoshan are 

separated stratigraphically by only 7–15 m (Yang and others, 2016), so both 

are considered producible from a single hydraulically fractured horizontal well. 

The Lower Jurassic Tight Oil AU includes those areas where the Da’anzhai or 

the Lianggaoshan, or both, are 15 m thick and not within a fold/thrust belt.

The Sichuan Basin was strongly influenced by Cenozoic uplift and erosion 

that caused leakage of hydrocarbons, a fundamental aspect of the geologic models 

for both AUs discussed above. The basin underwent 1.3–4.0 kilometers of 

uplift in the past 40 million years (Richardson and others, 2008). Fracturing 

and faulting associated with this late uplift broke up the strata along the basin 

margins (especially the northwest margin) and affected the central part of the 

basin to a lesser degree. There is a hydrocarbon leakage risk associated with 

this late fracturing and faulting.

Continuous oil and gas accumulations in the United States were used as analogs in this assessment. Table 1 lists the principal input data used for the assessment. 

SHAANXI

PROVINCE

SICHUAN

PROVINCE

Chongqing

Municipality

HUBEI

PROVINCE

HUNAN

PROVINCE

GUIZHOU

PROVINCE

YUNNAN

PROVINCE

GANSU

PROVINCE

CHINA

Chengdu

Chongqing

34° N

32° N

30° N

28° N

26° N

104° E 106° E 108° E 110° E

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

SOUTH

CHINA

SEA

CHN

IND Map

area

MMR

LAO

THA

VNM

0 50 100 KILOMETERS

0 50 100 MILES

EXPLANATION

Lower Jurassic Tight Oil AU

Sichuan Basin boundary

Triassic Xujiahe Tight Gas AU

Figure 1. Map showing location of the Sichuan Basin, China, and the locations of

the Triassic Xujiahe Tight Gas and Lower Jurassic Tight Oil Assessment Units (AUs). 
Undiscovered Resources Summary

The USGS quantitatively assessed continuous oil and gas resources 

in two Mesozoic AUs in the Sichuan Basin of China (table 2). For continuous 

gas resources, the estimated mean total is 29,065 billion cubic feet of gas (BCFG), 

or 29.1 trillion cubic feet of gas, with an F95–F5 range from 5,605 to 68,955 BCFG. 

For continuous oil resources, the estimated mean total is 1,227 million barrels 

of oil (MMBO), or 1.2 billion barrels of oil, with an F95–F5 range from 

268 to 2,743 MMBO. The estimated mean total for natural gas liquids is 

138 million barrels (MMBNGL) with an F95–F5 range from 25 to 338 MMBNGL. 

These resource estimates are for undiscovered, technically recoverable 

gas, oil, and natural gas liquids resources and do not reflect economically 

recoverable resources.

Table 1. Key input data for two continuous assessment units in the Sichuan Basin, China.

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

defined partly using U.S. tight-oil 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

Triassic Xujiahe Tight Gas AU Lower Jurassic Tight Oil AU

Minimum Mode Maximum Calculated mean Minimum Mode Maximum Calculated mean

Potential production area of AU (acres) 1,000 4,000,000 16,400,000 6,800,333 1,000 4,500,000 11,800,000 5,433,667

Average drainage area of wells (acres) 40 80 120 80 120 160 200 160

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

Area untested in AU (%) 80 90 95 88.3 70 80 90 80

Average EUR (BCFG, gas; MMBO, oil) 0.2 0.7 1.5 0.734 0.04 0.085 0.2 0.091

AU probability 1.0 1.0

Table 2. Results for two continuous assessment units in the Sichuan 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

Triassic Total Petroleum System

Triassic Xujiahe Tight Gas AU 1.0 Gas 5,404 23,338 66,666 28,082 20 91 275 112

Jurassic Total Petroleum System

Lower Jurassic Tight Oil AU 1.0 Oil 268 1,062 2,743 1,227 201 827 2,289 983 5 22 63 26

Total undiscovered continuous resources 268 1,062 2,743 1,227 5,605 24,165 68,955 29,065 25 113 338 138

References Cited

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.

Chen Shijia, Zhang Huanxu, Lu Jungang, Yang Yueming, Liu Chaowei, Wang Li, Zou Xianli, 

Yang Jiajing, Tang Haiping, Yao Yitong, Huang Youlin, Ni Shuai, and Chen Yingying, 2015, 

Controlling factors of Jurassic Da’anzhai Member tight oil accumulation and high production in central Sichuan Basin, SW China: Petroleum Exploration and Development, 

v. 42, no. 2, p. 206–214.

Li Zhongping, Huang Fangyan, He Xinwei, Zhang Wanlong, and He Yuting, 2014, Shale-gas 

reservoir-prediction study in Daanzhai, eastern Sichuan Basin: The Leading Edge, v. 33, 

no. 5, p. 526–534. 

Potter, C.J., 2018, Paleozoic shale gas resources in the Sichuan Basin, China: American 

Association Petroleum Geologists Bulletin, v. 102, no. 6, p. 987–1009. [Also available at 

https://doi.org/10.1306/0828171607817072.]

Potter, C.J., Schenk, C.J., Charpentier, R.R., Gaswirth, S.B., Klett, T.R., Leathers, H.M., Brownfield, 

M.E., Mercier, T.J., Tennyson, M.E., and Pitman, J.K., 2015, Assessment of Paleozoic shale gas 

resources in the Sichuan Basin of China, 2015: U.S. Geological Survey Fact Sheet 2015–3053, 

4 p. [Also available at https://doi.org/10.3133/fs20153053.]

Qin Shengfei, Li Feng, Li Wei, Zhou Zheng, and Zhou Guoxiao, 2018, Formation mechanism 

of tight coal-derived-gas reservoirs with medium-low abundance in Xujiahe Formation, 

central Sichuan Basin, China: Marine and Petroleum Geology, v. 89, part 1, p. 144–154. 

[Also available at https://doi.org/10.1016/j.marpetgeo.2017.06.032.]

Richardson, N.J., Densmore, A.L., Seward, D., Fowler, A., Wipf, M., Ellis, M.A., Yong Li, 

and Zhang, Y., 2008, Extraordinary denudation in the Sichuan Basin—Insights from 

low-temperature thermochronology adjacent to the eastern margin of the Tibetan Plateau: 

Journal of Geophysical Research, v. 113, B04409, 23 p. [Also available at https://doi.org/

10.1029/2006JB004739.]

Yang Yueming, Yang Jiajing, Yang Guang, Tao Shizhen, Ni C., Zhang Bin, He X., Lin Jianping, 

Huang Dong, Liu Min, and Zou Juan, 2016, New research progress of Jurassic tight oil 

in central Sichuan Basin, SW China: Petroleum Exploration and Development, v. 43, 

no. 6, p. 954–964. 

Zhao Wenzhi, Bian Congsheng, and Xu Zhaohui, 2013, Similarities and differences between natural 

gas accumulations in Sulige gas field in Ordos basin and Xujiahe gas field in Central Sichuan 

Basin: Petroleum Exploration and Development, v. 40, no. 4, p. 429–438.

Zhao Wenzhi, Wang Hongjun, Xu Chunchun, Bian Congsheng, Wang Zecheng, and Gao 

Xiaohui, 2010, Reservoir-forming mechanism and enrichment conditions of the extensive 

Xujiahe Formation gas reservoirs, central Sichuan Basin: Petroleum Exploration and 

Development, v. 37, no. 2, p. 146–157.

Zhu Guangyou, Gu Lijing, Su Jin, Dai Jinxing, Ding Wenlong, Zhang Jinchuan, and Song Lichen, 

2012, Sedimentary association of alternated mudstones and tight sandstones in China’s oil and 

gas bearing basins and its natural gas accumulation: Journal of Asian Earth Sciences, v. 50, 

p. 88–104. [Also available at https://doi.org/10.1016/j.jseaes.2012.01.008.]

Zou Caineng, 2017, Unconventional petroleum geology (second edition): Amsterdam, 

Elsevier, 500 p.

Zou Caineng, Gong Yanjie, Tao Shizhen, and Liu Shaobo, 2013, Geological characteristics and 

accumulation mechanisms of the “continuous” tight gas reservoirs of the Xu2 Member in 

the middle-south transition region, Sichuan Basin, China: Petroleum Science, v. 10, no. 2, 

p. 171–182. [Also available at https://doi.org/10.1007/s12182-013-0264-7.]

Zou Caineng, Tao Shizhen, Zhu Rukai, Yuan Xuanjun, Li Wei, Zhang Guangya, Zhang 

Xiangxiang, Gao Xiaohui, Liu Liuhong, Xu Chunchun, Song Jiarong, and Li Guohui, 

2009, Formation and distribution of “continuous” gas reservoirs and their giant gas 

province—A case from the Upper Triassic Xujiahe Formation giant gas province, Sichuan 

Basin: Petroleum Exploration and Development, v. 36, no. 3, p. 307–319.

Sichuan 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.

ISSN 2327-6916 (print) ISSN 2327-6932 (online) https://doi.org/10.3133/fs20193010