U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2015–3072

November 2015

Using a geology-based assessment methodology, the U.S. 

Geological Survey estimated means of 459 million barrels of shale 

oil, 275 billion cubic feet of associated gas, and 23 million barrels 

of natural gas liquids in the Central Sumatra Basin, Indonesia.

of uncertainty on the extent of source rock facies within the grabens, thermal maturation of the source rock, and retention of oil 

following the phases of compressional deformation in the basin.

The assessment input data for the Central Sumatra Basin 

Brown Shale Continuous Oil Assessment Unit (AU) are summarized in table 1. Input data for drainage areas of wells, success 

ratios, and estimated ultimate recoveries (EURs) of wells are 

taken from geologic analogs, including the lacustrine petroleum 

system of the Green River Formation in the Uinta Basin, Utah.

100° 101° 102° 103°

3°

2°

1°

0°

–1°

–2°

SUMATRA

MALAYSIA

SINGAPORE

Source: National Park Service

MALAYSIA

Area of

study

SUMATRA

JAVA

BORNEO

EXPLANATION

Central Sumatra Basin Province

Brown Shale Continuous Oil AU 

INDIAN

OCEAN

SOUTH

CHINA

SEA

STRAIT OF MALACCA

0 50 100 KILOMETERS

0 50 100 MILES

International boundary

Introduction

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

the potential for undiscovered technically recoverable unconventional oil and gas resources in the Central Sumatra Basin, Indonesia (fig. 1). Since the 1940s, exploration for conventional oil and 

gas has resulted in the discovery of more than 200 fields, most 

being oil fields. Undiscovered conventional oil and gas resources 

were previously assessed (Schenk and others, 2010). The focus of 

this study is the geologic evaluation and assessment of potential 

shale-oil (continuous) resources in the Central Sumatra Basin.

The Central Sumatra Basin represents one of a series of 

back arc basins associated with subduction along the Sumatra margin. The Sumatra back-arc realm underwent a phase of 

rifting in the Eocene to early Oligocene that formed a series of 

grabens (Robinson and Kamal, 1988). The grabens were filled 

with typical synrift nonmarine facies, including fluvial, deltaic, marginal lacustrine sandstones, and shallow to deep-water 

lacustrine shales. The principal petroleum source rock is the 

Oligocene Brown Shale of the Pemantang Group, an organicrich lacustrine shale known to have sourced most the oil and 

gas in the basin (Williams and others, 1985; Katz and Dawson, 

1997). Following cessation of rifting, thermal relaxation led to a 

sag phase, increased accommodation space and further deposition, which served to increase the thermal maturity of synrift, 

organic-rich, lacustrine source rocks. Compression from middle 

Miocene to Holocene related to subduction dynamics resulted in 

numerous structures within the basin, many of which form traps 

for conventional oil accumulations. The phases of compression 

are significant to this study as compression may have aided oil 

migration, thus reducing volumes of oil within the Brown Shale 

source-reservoir system.

For this assessment, an unconventional, or continuous 

source-reservoir rock system must: (1) contain greater than 

2 weight percent total organic carbon (TOC); (2) be within the 

proper thermal maturity window for oil generation; (3) have 

greater than 15 meters of organic-rich shale; and (4) contain 

Type I or Type II organic matter (Charpentier and Cook, 2011). 

Using these criteria, the USGS defined a Brown Shale–Sihapas 

Total Petroleum System in the Central Sumatra Basin (Schenk 

and others, 2010), and a Brown Shale Continuous Oil Assessment Unit for this study. The range of uncertainty on the 

potential area of the assessment unit (table 1) reflects the level 

Figure 1. Location of the Central Sumatra Basin, Indonesia.

National and Global Petroleum Assessment

Assessment of Shale-Oil Resources of the Central Sumatra 

Basin, Indonesia, 2015
Resource Summary

The USGS quantitatively assessed oil and associated gas 

resources in the Brown Shale Continuous Oil Assessment Unit 

(table 2). For undiscovered, technically recoverable resources, 

the mean totals are: 459 million barrels of shale oil (MMBO), 

with a fractile range from 72 to 1,196 MMBO (F95-F5, respectively); 275 billion cubic feet of associated gas (BCFG), with a 

fractile range from 41 to 740 BCFG (F95-F5); 23 million barrels 

of natural gas liquids (MMBNGL), with a fractile range from 3 

to 64 MMBNGL (F95-F5).

Using mean potential AU area, drainage area, and success 

ratio (table 1) an estimated mean of about 5,200 hydraulically 

fractured wells would be required to exploit the potential continuous oil resource.

For Further Information

Assessment results are available at the USGS Energy 

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

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, 75 p. http://pubs.usgs.

gov/of/2011/1167/. 

Katz, B.J., and Dawson, W.C., 1997, Pemantang–Sihapas 

petroleum system of Central Sumatra, in Proceedings of the 

International Conference on Petroleum Systems of SE Asia 

and Australasia, 1997: Indonesian Petroleum Association, 

Paper IPA97–PO–07, p. 685–698.

Robinson, K.M., and Kamal, Asril, 1988, Hydrocarbon generation, migration, and entrapment in the Kampar Block, Central 

Sumatra, in Proceedings of the 17th Annual Convention, 

Indonesian Petroleum Association, Paper IPA 88–11–10, 

p. 211–256.

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

Klett, T.R., Kirschbaum, M.A., Pitman, J.K., and Pollastro, 

R.M., 2010, Assessment of undiscovered oil and gas resources 

of southeast Asia, 2010: U.S. Geological Survey Fact 

Sheet 2010–3015, 4 p.

Williams, H.H., Kelley, P.A., Janks, J.S., and Christensen, R.M., 

1985, The Paleogene rift basin source rocks of Central Sumatra, in Proceedings of the 14th Annual Convention, Indonesian 

Petroleum Association, October 1985, p. 57–90.

Central Sumatra Basin Assessment Team

Christopher J. Schenk, Ronald R. Charpentier, 

Timothy R. Klett, Marilyn E. Tennyson, Tracey J. Mercier, 

Michael E. Brownfield, Janet K. Pitman, Stephanie B. Gaswirth, 

and Heidi M. Leathers-Miller.

ISSN 2327-6916 (print) ISSN 2327-6932 (online) http://dx.doi.org/10.3133/fs20153072

Table 1. Key assessment input data for the Brown Shale Continuous Oil Assessment Unit in the 

Central Sumatra Basin, Indonesia.

[EUR (estimated ultimate recovery per well), well drainage area, and success ratios are from U.S. shale-gas and 

shale-oil analogs. MMBO, million barrels of oil; BCFG, billion cubic feet of gas; AU, assessment unit, %, percent. The average EUR input is the minimum, median (not the mode), maximum, and calculated mean]

Assessment input data

Brown Shale Continuous Oil AU

Minimum Mode Maximum Calculated 

mean

Potential production area of AU (acres) 3,967 603,000 3,967,000 1,524,656

Average drainage area of wells (acres) 80 160 220 153

Success ratios (%) 10 50 90 50

Average EUR (MMBO, oil; BCFG, gas) 0.04 0.08 0.3 0.092

Table 2. Assessment results for Brown Shale Continuous Oil Assessment Unit in the Central Sumatra Basin, Indonesia.

[MMBO, million barrels of oil; 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. 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 Unit (AU)

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

Brown Shale–Sihapas TPS

Brown Shale Continuous Oil 

AU (38080161) 1.0 Oil 72 354 1,196 459 41 206 740 275 3 17 64 23

Total unconventional

resources 72 354 1,196 459 41 206 740 275 3 17 64 23