National and Global Petroleum Resource Assessment Project

Assessment of Paleozoic Shale Gas Resources in the Sichuan 

Basin of China, 2015

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2015–3053

October 2015

ISSN 2327-6916 (print) ISSN 2327-6932 (online)

http://dx.doi.org/10.3133/fs20153053

Using a geology-based assessment methodology, the U.S. Geological Survey estimated a mean of 23.9 trillion 

cubic feet of technically recoverable shale gas resources in Paleozoic formations in the Sichuan Basin of China.

sourced significant conventional oil and 

gas accumulations (Borjin and others, 

2014). The overlying uppermost Permian 

Dalong Formation also contains organicrich marine shale and was assessed with 

the Longtan. The Cambrian, OrdovicianSilurian, and Permian organic shales constitute three separate petroleum systems. 

The focus of this assessment is the 

potential for gas retained in these source 

rocks following oil generation and cracking. Conventional oil and gas resources 

of six Chinese provinces, including the 

Sichuan, were assessed by the USGS 

in 2011 (U.S. Geological Survey World 

Assessment Team, 2012).

Introduction

The U.S. Geological Survey (USGS) 

quantitatively assessed the potential for 

unconventional (continuous) gas resources 

within organic-rich shales in three 

Paleozoic stratigraphic intervals in the 

Sichuan Basin of China (fig. 1). The stratigraphic intervals are the Lower Cambrian 

Qiongzhusi Formation, the Upper 

Ordovician and lower Silurian Wufeng 

and Longmaxi Formations, and the upper 

Permian Longtan and Dalong Formations 

(fig. 2). Organic-rich shales of these formations have been demonstrated to be the 

principal source rocks for conventional oil 

and gas fields in the Sichuan Basin (Ryder 

and others, 1994; Dai and others, 2008; 

Borjin and others, 2014). Since 2008, there 

have been numerous investigations and 

tests of shale gas potential of Cambrian, 

uppermost Ordovician, and lower Silurian 

shales in the Sichuan Basin (Zou and 

others, 2010). Commercial production 

of shale gas from the Silurian Longmaxi 

Formation in the southeastern foldbelt 

(east of Chongqing, fig. 1) has been 

ongoing since late 2012 (Guo and Zhang, 

2014; Guo, 2015).

The organic-rich shales of the 

Qiongzhusi, Wufeng, and Longmaxi 

Formations were deposited in deep marine 

depocenters on the continental shelf off the 

South China continental block and near the 

early Paleozoic Gondwana margin. The 

shales presently contain up to 8 weight 

percent of Type II organic matter, averaging between 1 and 5.5 weight percent 

(Zou and others, 2010). The Longtan 

Formation is generally recognized as a 

coal-bearing marginal marine to deltaic 

source rock but has been demonstrated 

to contain a substantial organic-rich deep 

marine facies that contains Type II organic 

matter. The Longtan Formation has also 

Figure 1. Map showing 

location of the Sichuan 

Basin and the northwestern 

boundary of the 

southeastern foldbelt.

103° 104° 105° 106° 107° 108° 109° 110° 111°

34°

33°

32°

31°

30°

29°

28°

27°

0 75 150 MILES

0 75 150 KILOMETERS

!

Chengdu

Chongqing

SHAANXI PROVINCE

GANSU PROVINCE

GUIZHOU PROVINCE

HUNAN 

PROVINCE

SICHUAN PROVINCE HUBEI

PROVINCE

YUNNAN 

PROVINCE

EXPLANATION

Sichuan Basin

Foldbelt boundary

Province boundary

!^

BAY

OF BENGAL

SOUTH

CHINA

SEA

PACIFIC

OCEAN

SEA 

OF

JAPAN

MONGOLIA

RUSSIA

CHINA

INDIA

KAZAKHSTAN

Study area

MAP LOCATION

 YELLOW SEA

Source: Esri, DigitalGlobe, GeoEye, 

Earthstar Geographics, CNES/Airbus DS, 

USDA, USGS, AEX, Getmapping, 

Aerogrid, IGN, IGP, swisstopo, and the 

GIS User Community
The USGS assessment methodology consists of a wellperformance approach (Charpentier and Cook, 2011) that 

recognizes the geologic variability within assessed reservoirs. 

For non-U.S. assessments, the USGS assesses shale-gas reservoirs 

that (1) contain greater than 2 weight percent total organic carbon 

(TOC), (2) are within the proper thermal maturity window for gas 

generation, (3) have greater than 15-meter thickness of organicrich shale, and (4) contain Type I or II oil-prone organic matter. 

Areas that do not meet these minimum criteria are unlikely to have 

significant resource potential without major technological improvements or major natural-gas price increases. Shale gas accumulations in the United States were used as analogs in this assessment. 

Analog data from U.S. accumulations included mean estimated 

ultimate recoveries from populations of shale gas wells and mean 

drainage areas of directionally drilled wells. Principal input data 

used in the assessment are listed in table 1.

We defined six assessment units (AUs): two each for the 

Cambrian, Silurian (including uppermost Ordovician), and 

Permian petroleum systems. For each of these stratigraphic 

intervals, we defined a relatively undeformed “platform” AU to 

the northwest of the southeastern foldbelt, and a “foldbelt” AU 

within the southeastern foldbelt (fig. 1). Accordingly, the AUs are: 

Cambrian Qiongzhusi Platform Shale Gas, Cambrian Qiongzhusi 

Foldbelt Shale Gas, Silurian Longmaxi Platform Shale Gas, 

Silurian Longmaxi Foldbelt Shale Gas, Permian Longtan Platform 

Shale Gas, and Permian Longtan Foldbelt Shale Gas. All AUs were 

quantitatively assessed.

Geologic Models for Assessment

The geologic models for the AUs parallel the tectonic history 

of the Sichuan Basin as follows: for the Cambrian and Silurian 

AUs, organic shale was deposited in deep basins associated with 

the passive continental margin of the south China block, which 

itself lay off the margin of the Gondwana supercontinent. As these 

basins accumulated greater thicknesses of sediment during the 

Paleozoic, the shale formations were deeply buried and generated 

oil. After the collision of the North and South China continental 

blocks in Triassic time, rapid and voluminous continental sedimentation accelerated the burial of shale formations and resulted 

in increased thermal maturity and cracking of oil to gas. Permian 

oil-prone organic-rich shale also accumulated in discrete basinal 

lows and generated oil (and later, gas) during Mesozoic continental 

sedimentation. Significant volumes of oil and gas from each of 

these Paleozoic source rocks migrated into shallower conventional 

traps; however, substantial volumes of gas remained in the shale 

formations to form the present shale gas accumulations.

Major Late Cretaceous and Tertiary uplift of the basin 

occurred in response to accretionary tectonics that included the 

Himalayan collision of India and Eurasia; related fracturing and 

faulting provided pathways for leakage of gas from shale reservoirs. In addition, development of widespread detachment folds 

and thrust faults in the southeastern fold belt likely produced the 

greatest gas leakage. In the AUs designated “foldbelt,” the shale 

reservoirs are expected to be successful only in the least deformed 

Figure 2. Simplified stratigraphic column for the Sichuan Basin, 

showing stratigraphic context of geologic formations that define the 

assessment units. Modified after Hao and others (2008), U.S. Geological 

Survey Geologic Names Committee (2010), and Zou and others (2010).

Geological

age Formation Lithology

Quaternary

Tertiary

Cretaceous

Jurassic

Triassic

Permian Longtan

Silurian

Ordovician

Cambrian

Sinian

Pre-Sinian Basement

Carboniferous

2.6 Ma

66

146

200

251

299

416

444

488

542

850

Dalong

Longmaxi

Wufeng

Qiongzhusi

S

S

S

S

S

Conglomerate

Sandstone

Mudstone

Limestone

Dolomite

Coal

Anhydrite

Shale

Source rock

Gas reservoir

EXPLANATION

S
Table 1. Key assessment input data for the Paleozoic shale gas assessment units in the Sichuan Basin, China.

[EUR (estimated ultimate recovery per well) and well drainage area are from U.S. shale gas analogs. BCFG, billion cubic feet of gas; 

AU, assessment unit; %, percent. The average EUR input is the minimum, median, maximum, and calculated mean]

Assessment Input Data–Continuous AUs Cambrian Qiongzhusi Platform Shale Gas Cambrian Qiongzhusi Foldbelt Shale Gas

Minimum Mode Maximum Calculated mean Minimum Mode Maximum Calculated mean

Potential production area of AU (acres) 10,000 1,625,000 14,000,000 5,211,667 10,000 2,800,000 7,000,000 3,270,000

Average drainage area of wells (acres) 120 150 180 150 120 150 180 150

Success ratios (%) 5 20 50 25 5 15 40 20

Average EUR (BCFG) 0.2 0.4 1 0.431 0.2 0.35 0.8 0.373

AU probability 1.0 1.0

Silurian Longmaxi Platform Shale Gas Silurian Longmaxi Foldbelt Shale Gas

Minimum Mode Maximum Calculated mean Minimum Mode Maximum Calculated mean

Potential production area of AU (acres) 10,000 1,368,000 5,487,000 2,288,333 10,000 3,000,000 10,000,000 4,336,667

Average drainage area of wells (acres) 120 150 180 150 120 150 180 150

Success ratios (%) 10 45 90 48.3 10 40 90 46.7

Average EUR (BCFG) 0.2 0.8 2 0.856 0.2 0.7 1.5 0.734

AU probability 1.0 1.0

Permian Longtan Platform Shale Gas Permian Longtan Foldbelt Shale Gas

Minimum Mode Maximum Calculated mean Minimum Mode Maximum Calculated mean

Potential production area of AU (acres) 5,000 1,000,000 7,200,000 2,735,000 5,000 500,000 2,227,000 910,667

Average drainage area of wells (acres) 120 150 180 150 120 150 180 150

Success ratios (%) 5 20 50 25 5 15 40 20

Average EUR (BCFG) 0.2 0.4 1 0.431 0.2 0.35 0.8 0.373

AU probability 1.0 1.0

Table 2. Assessment results for continuous gas resources in the Sichuan Basin, China.

[BCFG, billion cubic feet of gas; MMBNGL, million barrels of natural gas liquids; TPS, total petroleum system; AU, assessment unit. 

Results shown are fully risked estimates. For gas accumulations, all liquids are included under the NGL (natural gas liquids) category. 

F95 represents a 95 percent chance of at least the amount tabulated. Other fractiles are defined similarly. Fractiles are additive under 

assumption of perfect positive correlation]

Total Petroleum System (TPS) 

and Assessment Units (AU)

AU

probability

Accumulation 

type

Total undiscovered resources

Gas (BCFG) NGL (MMBNGL)

F95 F50 F5 Mean F95 F50 F5 Mean

Cambrian TPS

Cambrian Qiongzhusi Platform Shale Gas AU 1.0 Gas 546 2,907 9,783 3,728 12 69 253 93

Cambrian Qiongzhusi Foldbelt Shale Gas AU 1.0 Gas 366 1,384 3,693 1,621 1 4 18 6

Silurian TPS

Silurian Longmaxi Platform Shale Gas AU 1.0 Gas 1,183 5,089 15,290 6,271 27 123 405 157

Silurian Longmaxi Foldbelt Shale Gas AU 1.0 Gas 2,016 8,258 23,462 9,875 3 25 108 36

Permian TPS

Permian Longtan Platform Shale Gas AU 1.0 Gas 307 1,530 5,054 1,953 7 37 131 49

Permian Longtan Foldbelt Shale Gas AU 1.0 Gas 87 368 1,100 452 0 1 5 2

Total undiscovered unconventional resources 4,505 19,536 58,382 23,900 50 259 920 343

areas, such as the Silurian shale reservoirs in the successful wells in the 

Jiaoshiba gas field east of Chongqing 

(fig. 1; Guo and Zhang, 2014; Guo, 

2015). In areas not affected by leakage along fault and fracture systems, 

overlying and underlying shales provide 

adequate roof and floor seals for the shale 

reservoirs. Exceptions might occur along 

the basal Cambrian unconformity beneath 

the Qiongzhusi Formation as well as 

mid-Permian and Permian-Triassic 

unconformities below and above the 

upper Permian shales, all of which would 

increase the risk of gas leakage. All shale 

reservoirs included in this assessment 

have sufficient brittle mineral content 

to be amenable to gas production by 

hydraulic fracturing.

Resource Summary

The USGS quantitatively assessed 

unconventional oil and gas resources 

in three Paleozoic shale sections in the 

Sichuan Basin of China. The mean total 

for unconventional gas resources is 

23,900 billion cubic feet (BCFG), with 

a range from 4,505 to 58,382 BCFG. 

The mean total for natural gas liquids 

is 343 million barrels (MMBNGL), 

with a range from 50 to 920 MMBNGL 

(table 2). These resource estimates are 

for undiscovered technically recoverable 

volumes of gas and natural gas liquids 

and do not reflect volumes of economically recoverable resources.

Of the mean unconventional gas 

total of 23,900 BCFG, 68 percent 

(16,146 BCFG) is estimated to be in the 

Silurian Longmaxi Platform Shale Gas 

and Silurian Longmaxi Foldbelt Shale 

Gas AUs, 22 percent (5,349 BCFG) 

is estimated to be in the Cambrian 

Qiongzhusi Platform Shale Gas and 

Cambrian Qiongzhusi Foldbelt Shale 

Gas AUs, and 10 percent (2,405 BCFG) 

is estimated to be in the Permian Longtan 

Platform Shale Gas and Permian Longtan 

Foldbelt Shale Gas AUs.
References Cited

Borjin, Tenger, Qin, Jianzhong, Fu, Xiaodong, Yang, 

Yunfeng, and Lu, Longfei, 2014, Marine hydrocarbon 

source rocks of the Upper Permian Longtan Formation and 

their contribution to gas accumulation in the northeastern 

Sichuan Basin, southwest China: Marine and Petroleum 

Geology, v. 57, p. 160–172.

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

for assessing continuous petroleum resources: U.S. Geological Survey Open-File Report 2011–1167, 75 p.

Dai, Jinxing, Zou, Caineng, Qin, Shengfei, Tao, Shizhen, 

Ding, Weiwei, Liu, Quanyou, and Hu, Anping, 2008, 

Geology of giant gas fields in China: Marine and Petroleum 

Geology, v. 25, p. 320–334.

Guo, Tonglou, 2015, The Fuling shale gas field—A highly 

productive Silurian gas shale with high thermal maturity 

and complex evolution history, southeastern Sichuan Basin, 

China: Interpretation, v. 3, no. 2, p. 1–10.

Guo, Tonglou, and Zhang, Hanrong, 2014, Formation and enrichment mode of Jiaoshiba shale gas field, Sichuan Basin: Petroleum Exploration and Development, v. 41, no.1, p. 31–40.

Hao, Fang, Guo, Tonglou, Zhu, Yangming, Cai, Xunyu, Zou, 

Huayao, and Li, Pingping, 2008, Evidence for multiple stages 

of oil cracking and thermochemical sulfate reduction in the 

Puguang gas field, Sichuan Basin, China: American Association of Petroleum Geologists Bulletin, v. 92, p. 611–637.

Ryder, R.T., Rice, D.D., Sun, Zhaocai, Zhang, Yigang, Qiu, 

Yunyu, and Guo, Zhengwu, 1994, Petroleum Geology of the 

Sichuan basin, China—Report on U.S. Geological Survey 

and Chinese Ministry of Geology and Mineral Resources 

field investigations and meetings, October 1991: U.S. Geological Survey Open-File Report 94–426, 67 p. 

U.S. Geological Survey Geologic Names Committee, 2010, 

Divisions of geologic time—Major chronostratigraphic 

and geochronologic units: U.S. Geological Survey Fact 

Sheet 2010–3059, 2 p.

U.S. Geological Survey World Energy Assessment Team, 

2012, Assessment of undiscovered conventional oil and 

gas resources of six geologic provinces of China, 2011: 

U.S. Geological Survey Fact Sheet 2012–3117, 4 p.

Zou, Caineng, Dong, Dazhong, Wang, Shejiao, Li, Jianzhong, 

Li, Xinjing, Wang, Yuman, Li, Denguha, and Cheng, 

Keming, 2010, Geological characteristics and resource 

potential of shale gas in China: Petroleum Exploration and 

Development, v. 37, no. 6, p. 641–653.

For Further Information

Assessment results are available at the USGS Energy 

Resources Program Web site, http://energy.usgs.gov/oilgas.

Sichuan Basin Assessment Team

Christopher J. Potter, Christopher J. Schenk, Ronald 

R. Charpentier, Stephanie B. Gaswirth, Timothy R. Klett, 

Heidi M. Leathers, Michael E. Brownfield, Tracey J. 

Mercier, Marilyn E. Tennyson, and Janet K. Pitman.

Fengdu Bridge, Yangtze River,

Chongqing municipality,

Sichuan Province. Photograph 

by Glabb (Wikimedia Commons; 

CC-BY-SA-3.0).