U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2015–3087

January 2016

National and Global Petroleum Assessment

Assessment of Undiscovered Continuous Gas Resources 

of the Ordos Basin Province, China, 2015

Using a geology-based assessment methodology, the U.S. Geological Survey estimated mean resources of 28 trillion cubic feet of tight 

gas and 5.6 trillion cubic feet of coalbed gas in upper Paleozoic rocks in the Ordos Basin Province, China.

Introduction

The U.S. Geological Survey quantitatively assessed 

the potential for technically recoverable resources of continuous (unconventional) natural gas in the Ordos Basin 

Province of China as part of the assessment of priority 

basins worldwide. Large volumes of tight gas and coalbed gas have been discovered and produced from upper 

Paleozoic rocks of the Ordos Basin Province. Data on 

the number of wells and well productivity are, however, 

publicly unavailable. Limited access to data contributed 

to the large uncertainty in the resource estimates.

The assessments were completed using a methodology developed by the U.S. Geological Survey. This methodology uses Monte Carlo simulation to calculate resource 

volumes based on probabilistic estimates of assessment 

unit (AU) area, average well drainage area, percent of AU 

area that is untested, well success ratio, average estimated 

ultimate recovery per well, and average coproduct ratios 

(Charpentier and Cook, 2010). Inadequate data pertaining to the numbers of wells and well productivity in the 

Ordos Basin Province required that these input distributions be based on the range of behavior in the complete set 

of analog tight gas and coalbed gas plays that have been 

assessed in the United States.

Two AUs were defined using published geologic 

studies and the IHS Energy (2014) database. The Upper 

Paleozoic Tight Gas AU covers 147,409 square kilometers of the central part of the Ordos Basin Province that 

gently dips (less than 1 degree) to the west (fig. 1). The 

western and southern boundaries of the AU are defined 

by fault zones. The northern boundary is defined as the 

transition between the gas-water zone and the updip 

water zone (Xiao and others, 2005). The eastern boundary, which separates the tight gas AU from the Upper 

Paleozoic Coalbed Gas AU, is the −1,200 meter subsurface depth contour. The sources of the gas are the coal 

beds in the Taiyuan and Shanxi Formations. Reservoirs 

are mainly low-permeability sandstones, especially in 

the Shanxi and lower Shihezi Formations. The accumulation is a basin-center, gas-charged zone with an updip 

water leg. Future potential is envisioned as extending 

into facies with poorer porosity and permeability than 

what is being currently developed.

Figure 1. Map showing the extent of the Ordos Basin Province, China, 

and the two assessments units defined in this study.

42°

40°

38°

36°

34°

104° 106° 108° 110° 112° 114°

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BAY

OF BENGAL

SOUTH

CHINA

SEA

PACIFIC

OCEAN

 YELLOW SEA

 SEA 

 OF

JAPAN

MONGOLIA

RUSSIA

CHINA

INDIA

KAZAKHSTAN

Area of

study

Map image is the intellectual property of Esri and is used herein 

under license. Copyright © 2015 Esri and its licensors. 

All rights reserved.

EXPLANATION

Upper Paleozoic Coalbed Gas 

 Assessment Unit

City

Ordos Basin Province

Upper Paleozoic Tight Gas 

 Assessment Unit

0 50 100 KILOMETERS

0 50 100 MILES

Xi-an
ISSN 2327-6916 (print) ISSN 2327-6932 (online) http://dx.doi.org/10.3133/fs20153087

Assessment input data

Upper Paleozoic Tight Gas Upper Paleozoic Coalbed Gas

Minimum Mode Maximum Calculated

mean

Minimum Mode Maximum Calculated

mean

Potential production area of AU 

(acres) 6,200,000 12,400,000 18,200,000 12,266,667 2,000,000 3,000,000 5,000,000 3,333,333

Average drainage area of wells 

(acres) 100 120 200 140 70 100 160 110

% area untested in AU 77 92 96 88 94 99 100 98

Success ratios (%) 30 50 90 57 25 50 95 57

Average EUR (BCFG) 0.2 0.6 1.4 0.637 0.1 0.3 1.0 0.337

AU probability 1.0 1.0

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

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

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

Total petroleum system and 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

Upper Paleozoic Tight Gas AU 1.0 Gas 13,172 25,831 50,005 27,964 25 60 147 70

Upper Paleozoic Coalbed Gas AU 1.0 Gas 2,302 4,960 11,311 5,622 0 0 0 0

Total undiscovered unconventional resources 15,474 30,791 61,316 33,586 25 60 147 70

Table 2. Assessment results for continuous gas resources in Ordos Basin Province, China.

[AU, assessment unit; 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 under the NGL 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 positve correlation. Shading indicates not applicable]

The Upper Paleozoic Coalbed Gas AU covers 24,410 square kilometers of the eastern part of the Ordos Basin Province (fig. 1). 

The eastern boundary of the AU is the basin structural boundary. The northern boundary is defined as the transition from the gas and 

water zone to the updip water zone (Xiao and others, 2005), which corresponds to the 0.8 percent coal vitrinite reflectance contour. 

The southern boundary is the 5-meter net-coal isopach. The western boundary, which separates the coalbed gas AU from the tight 

gas AU, is the −1,200 meter subsurface depth contour. The coals in the Taiyuan and Shanxi Formations are both the source of the 

gas and the reservoir.

The assessment input data for the two AUs are summarized in table 1.

Resource Summary

Resource estimates are summarized in table 2. The mean 

resource estimates for the Upper Paleozoic Tight Gas AU are 

27,964 billion cubic feet of gas (BCFG), with a F95 to F5 fractile 

range from 13,172 to 50,005 BCFG, respectively and 70 million 

barrels of natural gas liquids (MMBNGL), with a F95 to F5 fractile 

range from 25 to 147 MMBNGL, respectively. The mean resource 

estimate for the Upper Paleozoic Coalbed Gas AU is 5,622 BCFG, 

with a F95 to F5 fractile range from 2,302 to 11,311 BCFG, respectively. The mean estimate of the number of wells that would be 

required to develop the resources in the tight gas and coalbed gas 

AUs are 44,880 and 17,258 wells, respectively.

References Cited

Charpentier, R.R., and Cook, T.A., 2010, Improved USGS methodology for assessing continuous petroleum resources: U.S. 

Geological Survey Data Series 547, 22 p. and model program, 

accessed November 5, 2015, at http://pubs.usgs.gov/ds/547/.

Ordos Basin Assessment Team 

Ronald R. Charpentier, Timothy R. Klett, Christopher J. Schenk, 

Michael E. Brownfield, Stephanie B. Gaswirth, Phuong A. Le, 

Heidi M. Leathers-Miller, Kristen R. Marra, and 

Tracey J. Mercier.

For Further Information

Assessment results are available at the U.S. Geological Survey 

Energy Program Web site at http://energy.usgs.gov/OilGas/.

IHS Energy, 2014, International petroleum exploration and production database: Englewood, Colo., IHS Energy.

Xiao, X.M., Zhao, B.Q., Thu, Z.L., Song, Z.G., and Wilkins, 

R.W.T., 2005, Upper Paleozoic petroleum system, Ordos Basin, 

China: Marine and Petroleum Geology, v. 22, p. 945–963.