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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 highto 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.

Assessment of Permian coalbed gas resources of the Karoo Basin Province, South Africa and Lesotho, 2016