U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2016–3089

December 2016 Printed on recycled paper

National and Global Petroleum Assessment

Assessment of Coalbed Gas Resources of the Central 

and South Sumatra Basin Provinces, Indonesia, 2016

Introduction

The U.S. Geological Survey (USGS) quantitatively 

assessed the potential for undiscovered, technically 

recoverable continuous coalbed gas resources in the 

Central and South Sumatra Basin Provinces, Indonesia 

(fig. 1). The USGS defined a Neogene Coal Total 

Petroleum System (TPS) in each of these basins and 

the Central Sumatra Neogene Coalbed Gas Assessment 

Unit (AU) and the South Sumatra Neogene Coalbed Gas 

AU. Minable areas of Neogene-age low-rank coal have 

been mapped in both basins (Adhi and others, 2004), 

and recent attempts have been made to exploit coalbed 

gas resources in the South Sumatra Basin (Sosrowidjojo 

and Saghafi, 2009). Much is known of Neogene coal 

thickness, petrography, geochemistry, gas content, and 

thermal maturity in these basins (Amijaya and Littke, 

2005; Davis and others, 2006; Sosrowidjojo and Saghafi, 

2009). Critical elements of the geologic models for this 

assessment include (1) the low rank of the coals (less 

than 0.5 percent vitrinite reflectance), (2) the presence 

of a biogenic gas system, and (3) the degree of gas 

saturation of the coals. This assessment does not include 

the potential for any thermally generated coalbed gas. 

All published information was leveraged in this study to 

define coalbed gas assessment units and quantitatively 

assess the potential for recoverable coalbed gas resources.

The Central and South Sumatra Basin Provinces 

represent backarc basins associated with subduction 

along the Sumatran margin. In the late Paleogene, the 

formation of the right-lateral Sumatran Fault by oblique 

convergence of the Australian plate with the Sumatran 

plate resulted in uplift of the Barisan Mountains. The 

Barisan Mountains are the source area for the regressive 

clastic wedge that prograded eastward across the Central 

and South Sumatra Basin Provinces. The Neogene 

coals of this study were deposited within this regressive 

clastic wedge.

Geologic Model for Assessment

The geologic model for this assessment is similar for 

continuous coalbed gas accumulations in both the Central 

and South Sumatra Basin Provinces. Coals of the Neogene 

regressive clastic wedge were deposited across both 

basins. Shallow burial left the coals thermally immature 

(except in proximity to intrusions), and thus of low rank. 

Using a geology-based assessment methodology, the U.S. Geological Survey estimated a mean of 20 trillion cubic feet of undiscovered, 

technically recoverable coalbed gas resources in the Central and South Sumatra Basin Provinces of Indonesia.

Figure 1. Map showing the location of the Central and South Sumatra Basin 

Provinces, Indonesia, and the two assessment units (AUs) defined in this study.

100° 105°

0°

–5°

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

MALAYSIA

INDONESIA

Sumatra

Java

Kalimantan

Borneo

Sulawesi

INDIAN

OCEAN

SOUTH

CHINA

SEA

SINGAPORE

Area

of study

EXPLANATION

Central Sumatra Neogene

 Coalbed Gas AU

South Sumatra Neogene

 Coalbed Gas AU

Provinces boundary

0 50 100 KILOMETERS

0 50 100 MILES

SINGAPORE

INDONESIA

Jambi

Padang

Palembang

Pekanbaru

South

Sumatra

MALAYSIA

INDIAN OCEAN

Central

Sumatra

Barisan Mountains

SUMATRAN FAULT
ISSN 2327-6916 (print) ISSN 2327-6932 (online) https://doi.org/10.3133/fs20163089

Bacterial activity produced biogenic gas 

in the coal, and measurements indicated 

that the coals are undersaturated with 

gas. The presence of liptinite led to coals 

having hydrogen indices as high as 

300 milligrams hydrocarbon per gram 

organic carbon, which suggests that the 

coals may be able to produce liquids 

(Davis and others, 2006). However, we did 

not assess potential liquids given the low 

rank of the coals.

The assessment input data are 

summarized in table 1. Data for 

drainage areas of wells, success ratios, 

and estimated ultimate recoveries 

for coalbed gas wells are taken from 

geologic analogs in the United States, 

particularly the biogenic coalbed gas 

accumulation in the Powder River 

Basin of Wyoming (Flores, 2004).

Undiscovered Resources Summary

The USGS quantitatively assessed 

undiscovered, technically recoverable 

continuous coalbed gas resources (table 2). 

References Cited

Adhi, R.N., Pujobroto, Agus, Gurusings, C.K.K., Kuntjara, Umi, Sunuhadi, D.N., Kasbani, Sumarna, Nandang, Sumaatmadja, E.R., Kusdarto, Zulfikar, 

Iskandar, and Wahyuningsih, Rina, 2004, National resources and reserves of mineral, coal, and geothermal: Indonesian Directorate General of Geology 

and Mineral Resources, Special Publication No. 103, 130 p.

Amijaya, Hendra, and Littke, Ralf, 2005, Microfacies and depositional environment of Tertiary Tanjung Enim low-rank coal, South Sumatra Basin, 

Indonesia: International Journal of Coal Geology, v. 61, nos. 3–4. p. 197–221.

Davis, R.C., Noon, S.W., and Harrington, J., 2006, The petroleum potential of Tertiary coals from Western Indonesia—Relationship to mire type and 

sequence stratigraphic setting: International Journal of Coal Geology, v. 70, nos. 1–3, p. 35–52.

Flores, R.M., 2004, Coalbed methane in the Powder River Basin, Wyoming and Montana—An assessment of the Tertiary–Upper Cretaceous Coalbed 

Methane Total Petroleum System, chap. 2 of USGS Powder River Basin Province Assessment Team, Total petroleum system and assessment of coalbed gas in the Powder River Basin Province, Wyoming and Montana: U.S. Geological Survey Digital Data Series DDS–69–C, one CD–ROM.

Sosrowidjojo, I.B., and Saghafi, A., 2009, Development of the first coal seam gas exploration program in Indonesia—Reservoir properties of the Muaraenim 

Formation, south Sumatra: International Journal of Coal Geology, v. 79, no. 4, p. 145–156.

Assessment input data—Continuous AUs

Central Sumatra Neogene Coalbed Gas AU Minimum Mode Maximum Calculated 

mean

Potential production area of AU (acres) 1,000 2,569,000 12,844,000 5,137,933

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

Success ratio (%) 50 60 70 60

Average EUR (BCFG) 0.08 0.2 0.35 0.206

AU probability 1.0

South Sumatra Neogene Coalbed Gas AU Minimum Mode Maximum Calculated 

mean

Potential production area of AU (acres) 1,000 4,076,000 16,302,000 6,792,833

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

Success ratio (%) 50 70 80 66.7

Average EUR (BCFG) 0.08 0.2 0.35 0.206

AU probability 1.0

Table 1. Key assessment input data for two continuous assessment units in the Central and 

South Sumatra Basin Provinces, Indonesia.

[AU, assessment unit; %, percent; EUR, estimated ultimate recovery per well; BCFG, billion cubic feet of gas. 

EUR, well drainage area, and success ratios are from U.S. coalbed gas and shale-gas analogs. The average EUR 

input is the minimum, median (not the mode), maximum, and calculated mean. Shading indicates not applicable]

Total petroleum system 

and assessment units (AUs)

AU

probability

Accumulation 

type

Total undiscovered resources

Gas (BCFG) NGL (MMBNGL)

F95 F50 F5 Mean F95 F50 F5 Mean

Neogene Coal Total Petroleum System

Central Sumatra Neogene Coalbed Gas AU 1.0 Gas 1,880 7,216 17,160 8,119 0 0 0 0

South Sumatra Neogene Coalbed Gas AU 1.0 Gas 2,989 10,677 24,829 11,921 0 0 0 0

Total undiscovered continuous resources 4,869 17,893 41,989 20,040 0 0 0 0

Table 2. Results for two continuous assessment units in the Central and South Sumatra Basin Provinces, Indonesia.

[BCFG, billion cubic feet of gas; 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]

The estimated mean total coalbed gas 

resource is 20,040 billion cubic feet of 

gas (BCFG), or 20 trillion cubic feet of 

gas, with an F95–F5 range from 4,869 to 

41,989 BCFG. For the Central Sumatra 

Neogene Coalbed Gas AU, the estimated 

mean resource is 8,119 BCFG with an 

F95–F5 range from 1,880 to 17,160 BCFG. 

For the South Sumatra Neogene Coalbed 

Gas AU, the estimated mean resource is 

11,921 BCFG with an F95–F5 range from 

2,989 to 24,829 BCFG. 

Sumatra Basins Assessment Team

Christopher J. Schenk, Timothy R. Klett, Marilyn E. Tennyson, Tracey J. Mercier, Michael E. Brownfield, Janet K. Pitman, 

Stephanie B. Gaswirth, and Thomas M. Finn

For More Information

Assessment results are available at the USGS Energy Resources Program Web site at http://energy.usgs.gov.