South Africa's Karoo Shale Gas Estimate Slashed
A new research article in a scholarly journal suggests that previous estimates of the shale gas potential in the country’s arid Karoo region may have been over-optimistic.
The report ‘Deflating the shale gas potential of South Africa’s Main Karoo basin’, published by the South African Journal of Science, suggests that earlier estimates by the US Energy Information Administration (EIA) in 2011 of a 485 trillion ft3 resource were “certainly grossly inflated.” That estimate was subsequently downgraded to about 390 trillion ft3.
However, the new research article puts the more likely figure at 49 trillion ft3 “but with a large uncertainty interval.” Lowest estimates give a technically recoverable shale gas resource of 13 trillion ft3.
“Measurements were recently conducted on samples from two boreholes and…these measurements indicate that there is little to no desorbed and residual gas, despite high total organic carbon values. Organic carbon in the shale is largely unbound to hydrogen, and little hydrocarbon generation potential remains," said the article written by Michiel de Kock and six colleagues.
In spite of the lowered expectations, the scientists suggest that such downgraded estimates still point to a large resource with developmental potential for the South African petroleum industry.
“To be economically viable, the resource would be required to be confined to a small, well-delineated ‘sweet spot’ area in the vast southern area of the basin. It is acknowledged that the drill cores we investigated fall outside of currently identified sweet spots and these areas should be targets for further scientific drilling projects.” They concluded that this is the first report of direct measurements of the actual gas contents of southern Karoo basin shales, and the findings reveal carbon content of shales to be dominated by over-mature organic matter.
Therefore, the results demonstrate “a much reduced potential shale gas resource.”
They suggested: “Proving this resource is crucial, and a very important next step is testing it within an identified sweet spot, as is currently planned by the Council for Geoscience through drilling of an additional scientific stratigraphic borehole near Beaufort West.”
The authors of the latest study hail from the University of Johannesburg’s Department of Geology, the South African Council for Geoscience, the School of Earth and Environmental Sciences at Portsmouth University, and the University of Cape Town’s Department of Geological Sciences.
Delegates at a conference a month ago said more work needs to be done to assess whether shale gas is, indeed, a feasible part of South Africa's future energy mix. Four months ago a senior government official said the country's first shale gas exploration licences, in the Karoo, might be awarded by late September but now that looks increasingly unlikely.
John Fraser, Johannesburg