National and Global Petroleum Assessment

Assessment of Permian Coalbed Gas Resources of the 

Karoo Basin Province, South Africa and Lesotho, 2016

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2016–3103

February 2017 Printed on recycled paper

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

mean resources of 5.27 trillion cubic feet of coalbed gas in the Karoo Basin Province.

Introduction

The U.S. Geological Survey (USGS) completed an assessment of 

undiscovered, technically recoverable coalbed gas resources within the 

Karoo Basin Province of South Africa and Lesotho (fig. 1). The Karoo 

Basin is a Permian retroarc foreland basin that formed as the Cape fold 

belt developed by subduction-related compression (Cadle and others, 

1993). As the Cape fold belt developed, thrust loading caused lithospheric 

subsidence, forming an asymmetric foreland basin that was deepest in the 

south and shallower to the north. In the southern foredeep, the Permian 

section is dominated by deep-water shales and sandstones, whereas to the 

north and northeast the Permian section contains fluvial-deltaic conglomerates, sandstones, shales, and coals (Cairncross, 2001; Hancox and Götz, 

2014). The focus of this study is the potential for coalbed gas resources in 

the coal-bearing sequences of the Vryheid Formation of the Ecca Group 

(fig. 2). The Vryheid Formation contains several coarsening-upward 

sequences with coals in the upper part of each sequence, and the coals 

can be traced throughout the study area (Hancox and Götz, 2014). Coal 

thickness is variable, but individual coals can be as much as 10-meters 

thick. Coal rank is reported to be high- to low-volatile bituminous with 

higher rank in the eastern part of the study area. Permian sedimentation 

in the Karoo Basin Province ended with extensive volcanism related to 

the breakup of the Gondwana supercontinent. Dolerites associated with 

volcanism might have had a negative impact on potential coalbed gas 

resources, although there are differing interpretations as to the impact of 

the intrusives (Gröcke and others, 2009; Hancox and Götz, 2014). Distal 

Ecca Group shales include the Whitehill and Prince Albert Formations, 

which contain potential shale-gas resources (Brownfield and others, 

2016), but the resource potential of shale gas may also have been affected 

by local thermal maturation and loss of gas by the emplacement of widespread intrusives.

Total Petroleum System and Assessment Units

For the Karoo Basin Province, the USGS defined a Vryheid Coal 

Total Petroleum System (TPS) and a Karoo Vryheid Coalbed Gas 

Assessment Unit (AU) within this TPS. The boundary of the AU is 

defined mainly by the Karoo Basin Province boundary in the northeastern part of the basin and by the 50-meter isopach contour of the Vryheid 

Formation for the southwestern boundary (fig. 3). The mined areas 

were removed from the total area of the AU. The major geologic risk 

for the occurrence of recoverable coalbed gas in this AU is retention of 

recoverable gas within the coals following emplacement of widespread 

intrusives. The geologic model proposed in this study is for some portion 

Figure 1. Location of the Karoo Basin Province, South Africa and 

Lesotho, and the coalbed gas assessment unit (AU) defined in this 

study. m, meter.

Figure 2. Stratigraphic column of Lower Permian units in the Karoo Basin 

Province, South Africa and Lesotho, with the Vryheid Formation and the 

correlative Collingham, Whitehill, and Prince Albert Formations (modified from 

Hancox and Götz, 2014). Black horizontal lines are coal seams.

Southern 

Karoo 

Basin

Age

Northeastern

Karoo 

Basin

Collingham Formation

Whitehill Formation

Prince

Albert

Formation

Artkinskian

Permian (part)

Sakmarian

Asselian

Pietermaritzburg 

Formation

Vryheid Formation

Ecca Group (part)

Dwyka Group

? ?

25° 26° 27° 28° 29° 30° 31° 32° 33°

–25°

–26°

–27°

–28°

–29°

–30°

–31°

–32°

Durban

Bloemfontein

PRETORIA

(TSHWANE)

Johannesburg

SOUTH 

AFRICA

SWAZILAND

BOTSWANA MOZAMBIQUE

INDIAN OCEAN

MASERU

50-m isopach LESOTHO

of Vryheid Formation

Maputo

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

AFRICA

Map

area

ATLANTIC

OCEAN

INDIAN

OCEAN

0 60 120 MILES

0 60 120 KILOMETERS

EXPLANATION

Karoo Vryheid Coalbed Gas AU

Karoo Basin Province boundary (part)
Figure 3. Isopach map of the Vryheid Formation in the northeastern part of 

the Karoo Basin Province, South Africa and Lesotho (modified from Hancox 

and Götz, 2014).

Assessment input data—Continuous AU Karoo Vryheid Coalbed Gas AU

Minimum Mode Maximum Calculated mean

Potential production area of AU (acres) 1,000 26,449,000 41,928,000 22,792,667

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

Success ratio (%) 5 20 35 20

Average EUR (BCFG) 0.04 0.08 0.3 0.092

AU probability 1.0

Table 1. Key assessment input data for one assessment unit in the Karoo Basin Province, South Africa and Lesotho.

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

success ratios are taken from U.S. coalbed gas analogs. The average EUR input is the minimum, median, maximum, and calculated mean. Shading indicates not applicable]

Total petroleum system 

and assessment unit (AU)

AU

probability

Accumulation

type

Total undiscovered resources

Gas (BCFG) NGL (MMBNGL)

F95 F50 F5 Mean F95 F50 F5 Mean

Vryheid Coal Total Petroleum System

Karoo Vryheid Coalbed Gas AU 1.0 Gas 1,207 4,540 11,870 5,271 0 0 0 0

Total undiscovered continuous 

resources 1,207 4,540 11,870 5,271 0 0 0 0

Table 2. Assessment results for one assessment unit in the Karoo Basin Province, South Africa and Lesotho.

[BCFG, billions of cubic feet of gas; MMBNGL, million barrels of natural gas liquids. 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 the assumption of perfect positive correlation. Shading indicates not applicable]

of the gas to have been retained within the coals following the intrusion of dolerites as the Gondwana supercontinent began to breakup in 

the Mesozoic.

Assessment input data for the Karoo Vryheid Coalbed Gas AU are 

shown in table 1. Well drainage areas, estimated ultimate recoveries, and 

success ratios were guided by U.S. coalbed gas analog assessment units.

Undiscovered Resources Summary

The USGS quantitatively assessed undiscovered continuous coalbed gas resources within the Karoo Basin Province (table 2). For coalbed 

gas resources, the estimated mean is 5,271 billion cubic feet of gas 

(BCFG), or 5.27 trillion cubic feet of gas, with an F95–F5 range from 

1,207 to 11,870 BCFG. The major source of geologic risk is the retention 

of gas in the coals following dolerite emplacement during the Mesozoic 

breakup of the Gondwana supercontinent.

References Cited

Brownfield, M.E., Schenk, C.J., Klett, T.R., Pitman, J.K., Tennyson, M.E., Gaswirth, S.B., 

Le, P.A., Leathers-Miller, H.M., Mercier, T.J., and Finn, T.M., 2016, Assessment of 

shale-gas resources of the Karoo Province, South Africa and Lesotho, Africa, 2016: 

U.S. Geological Survey Fact Sheet 2016–3038, 2 p.

Cadle, A.B., Cairncross, Bruce, Christie, A.D.M., and Roberts, D.L., 1993, The Karoo 

Basin of South Africa—Type basin for the coal-bearing deposits of southern Africa: 

International Journal of Coal Geology, v. 23, nos. 1–4, p. 117–157.

Cairncross, Bruce, 2001, An overview of the Permian (Karoo) coal deposits of southern 

Africa: Journal of African Earth Sciences, v. 33, nos. 1–3, p. 529–562.

Gröcke, D.R., Rimmer, S.M., Yoksoulian, L.E., Cairncross, Bruce, Tsikos, Harilaos, and

van Hunen, Jeroen, 2009, No evidence for thermogenic methane release in coal from 

the Karoo–Ferrar large igneous province: Earth and Planetary Science Letters, v. 277, 

nos. 1–2, p. 204–212.

Hancox, P.J., and Götz, A.E., 2014, South Africa’s coalfields—A 2014 perspective: 

International Journal of Coal Geology, v. 132, p. 170–254.

Karoo Basin Province Assessment Team

ISSN 2327-6916 (print) ISSN 2327-6932 (online) https://doi.org/10.3133/fs20163103

Christopher J. Schenk, Michael E. Brownfield, 

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

Mercier, Sarah J. Hawkins, Stephanie B. Gaswirth, 

Kristen R. Marra, Thomas M. Finn, Phuong A. Le, 

and Heidi M. Leathers-Miller

For More Information

Assessment results also are available at 

the USGS Energy Resources Program website 

at http://energy.usgs.gov.

Southern limit of the Vryheid Formation

Preservation limit of the Karoo strata

Present day coastline

Bloemfontein

Welkom

Harrismith

Johannesburg

Harding

Durban

Newcastle

Vryheid

Volksrust

200

200

100 100

100 100

100

100

50

500

0

0

50

0

50

0

0

50

100

200

300

400

500

0 50 100 MILES

0 50 100 KILOMETERS

500

400

300

200

100

50

0

Vryheid Formation isopach,

in meters

EXPLANATION