National and Global Petroleum Assessment

Assessment of Coalbed Gas Resources of the Kalahari Basin 

Province of Botswana, Zimbabwe, and Zambia, Africa, 2016

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2017–3003

February 2017 Printed on recycled paper

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

mean resources of 4.5 trillion cubic feet of coalbed gas in the Kalahari Basin Province of Botswana, Zambia, and Zimbabwe, Africa.

Introduction

The U.S. Geological Survey (USGS) 

completed an assessment of undiscovered, 

technically recoverable continuous (unconventional) coalbed gas resources within the Kalahari 

Basin Province (fig. 1), a geologically complex 

region of approximately 648,670 square kilometers in Botswana, Zambia, and Zimbabwe. 

As much as 1,500 meters (m) of Lower Permian 

sedimentary rocks are present in the Kalahari 

Basin Province. Coals are present in the Permian 

Ecca Group. Thickness of the coal-bearing 

zone ranges from 500 to 550 m with net coal 

thickness ranging from 55 to 125 m. Individual coalbeds range from 1 m to as much as 

30 m thick.

Twenty-six coalbed gas exploration 

wells have been drilled in the Kalahari Basin 

Province, and several test wells in Botswana and 

Zimbabwe reported recoverable gas content or 

production (IHS MarkitTM, 2015; McConachie, 

2015; Dowling, 2016). Gas contents are as 

much as 9.5 cubic meters per ton (334 standard 

cubic feet per ton) with gas content increasing 

with depth.

Total Petroleum System 

and Assessment Units

For the Kalahari Basin Province, 

the USGS defined the Permian Composite 

Total Petroleum System (TPS) and the Kalahari 

Coalbed Gas Assessment Unit (AU) within this 

TPS. Coalbed gas production tests from several 

wells in the province provide limited but good 

evidence that this petroleum system is viable. 

Coalbed gas is known to exist in the Kalahari 

and Zambezi Basins of Botswana, Zambia, and 

Zimbabwe (Dowling and others, 2016).

Figure 1. Location of the Kalahari Basin Province and the coalbed gas assessment unit 

(AU) defined in this study.

The Kalahari Coalbed Gas AU is defined as an area containing thick coals 

in the Ecca Group and where the coals are less than 1,800 m below the surface. 

Coals in the Zambia and Zimbabwe parts of the province (also called the Zambezi 

Basin) range from subbituminous to medium-volatile bituminous coal to highvolatile bituminous, whereas coal rank in the Botswana part of the Kalahari Basin 

18° 24° 30°

–16°

–22°

–28°

Durban

MAPUTO

LUSAKA

HARARE

PRETORIA

(TSHWANE) Johannesburg

GABORONE

NAMIBIA

SOUTH AFRICA

BOTSWANA

ZAMBIA

ZIMBABWE

ANGOLA

MOZAMBIQUE

LESOTHO

SWAZILAND

INDIAN 

OCEAN

Kalahari Basin

Zambezi Basin

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

AFRICA

Map

area

ATLANTIC

OCEAN

INDIAN

OCEAN

0 125 250 MILES

0 125 250 KILOMETERS

EXPLANATION

Kalahari Coalbed Gas AU

Kalahari Basin Province boundary
ISSN 2327-6916 (print) ISSN 2327-6932 (online) https://doi.org/10.3133/fs20173003

Province is high-volatile bituminous 

(Cairncross, 2001). Coals in Botswana 

exhibit vitrinite reflectance (Ro) values 

ranging from 0.5 to 0.7 percent Ro, 

a high ash content averaging 39 percent, and sulfur content averaging 

0.45 percent. Coalbeds in Botswana 

have been thermally elevated in rank 

by dolerite intrusions within the Ecca 

Group, whereas in Zimbabwe, there 

are few dolerite intrusions to influence 

References Cited

Cairncross, Bruce, 2001, An overview of the Permian (Karoo) coal deposits of southern Africa: Journal of African Earth Sciences, 

v. 33, nos. 3–4, p. 529–562.

Dowling, G.J., 2016, CBM potential of RSA, Botswana & Zimbabwe, in Fossil Fuel Foundation (FFF) Workshop, Johannesburg, South 

Africa, May 11, 2016, Proceedings: Fossil Fuel Foundation, accessed September 13, 2016, at http://www.fossilfuel.co.za/courses/2016/

Gas-Workshop/3/CBM-Potential-RSA-Bots-Zim-FFF-11th-May_greg-dowling.pdf.

IHS MarkitTM, 2015, International petroleum exploration and production database [current through December 2015]: IHS Markit, 

15 Inverness Way East, Englewood, CO 80112.

McConachie, Bruce, comp., 2015, Independent geologist’s report CBM licenses in Botswana: Brisbane, Queensland, Australia, 

Tlou Energy, and London, United Kingdom, Brandon Hill Capital and Grant Thornton, 53 p., accessed September 13, 2016, at 

http://tlouenergy.com/wp-content/uploads/2015/10/Tlou_AIM_Admission_Competent-Persons-Report.pdf. [Prepared by SRK 

Consulting (Australasia), Brisbane, Queensland, Australia, project number TLO004.]

Assessment input data

Kalahari Coalbed Gas AU

Minimum Mode Maximum Calculated mean

Potential production area of AU (acres) 10,000 4,000,000 50,000,000 18,003,333

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

Success ratios (%) 10 20 35 21.7

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 Kalahari Basin Province, Africa.

[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. shalegas and shale-oil 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

Permian Composite Total Petroleum System

Kalahari Coalbed Gas AU 1.0 Gas 622 3,523 11,721 4,504 0 0 0 0

Total undiscovered resources 622 3,523 11,721 4,504 0 0 0 0

Table 2. Assessment results for one assessment unit in the Kalahari Basin Province, Africa.

[BCFG, billion cubic feet of gas; MMBNGL, million barrels of natural gas liquids. Results shown are fully risked estimates. For gas accumulations, all liquids are included 

in 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]

coal rank. Kalahari Basin (Botswana) 

coals contain thermogenic methane, 

whereas Zambezi Basin (Zambia and 

Zimbabwe) coals contain biogenic gas 

(low-rank coals) and thermogenic gas 

(high-rank coals).

Assessment input data for the 

Kalahari Coalbed Gas AU are shown in 

table 1. Well drainage areas, estimated 

ultimate recoveries, and success ratios 

are guided by U.S. coalbed gas analogs.

Undiscovered Resources Summary

The USGS quantitatively assessed 

coalbed gas resources within one coalbed gas assessment unit in the Kalahari 

Basin Province (table 2). For coalbed gas 

resources, the estimated mean totals for the 

Kalahari Coalbed Gas AU are 4,504 billion cubic feet of gas (BCFG), or 4.5 trillion cubic feet of gas, with an F95–F5 

range from 622 to 11,721 BCFG.

Kalahari Basin Province Assessment Team

Michael E. Brownfield, Christopher J. Schenk, Timothy R. Klett, Marilyn E. 

Tennyson, Tracey J. Mercier, Stephanie B. Gaswirth, Kristen R. Marra, Sarah J. Hawkins, 

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.