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The Petroleum Potential of South Africa's Onshore Karoo Basins*

 

Lindiwe Raseroka1 and Ian R. McLachlan1

 

Search and Discovery Article #10196 (2009)

Posted June 5, 2009

 

*Adapted from expanded abstract prepared for AAPG International Conference and Exhibition, Cape Town, South Africa, October 26-29, 2008.

 

1Frontier Geology, Petroleum Agency SA, Cape Town, South Africa ([email protected] )

 

Abstract

 

The Late Carboniferous to Mid-Jurassic Karoo basins hold an important place in South African geology and economics as they occupy more than half of the nation's land area and host the coal deposits that provide most of the country's energy. Together with the gold in the underlying Archean Witwatersrand deposits they have provided the focus for the development of South Africa's industrial heartland. As yet very little systematic modern exploration for petroleum has been done - the opportunity exists for a new generation of explorers to test the potential of these huge basins.

 

The Great Karoo basin covers an area of over 700,000 km2 and constitutes a retro-arc foreland basin. (Figure 1) Maximum down-warping occurred in the south where cumulative sediment thickness reached 12 km. South Africa's main coal deposits occur in an arc across the northern flank of the basin but major reserves are also contained in the smaller fault controlled basins that lie to the north.

 

Promising petroleum exploration plays include:

  • Coal-bed methane
  • Conventional gas
  • Unconventional, possibly biogenic gas (associated with high concentrations of helium - up to 26%) that occurs in the Witwatersrand Group and other ancient basement rocks in the Welkom and Evander gold field areas.
  • Deep tight shale gas
  • Conventional oil

 

The present energy shortfall in South Africa provides a new impetus for the development of an expanded natural gas industry.

 

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Figure 1. Onshore Karoo basins: exploration activity.

Discussion

 

The present energy shortfall in South Africa is providing a new impetus to petroleum exploration. Already there are 26 current exploration rights (four of which are old order rights awaiting conversion under the new Minerals and Petroleum Resources Development Act of 1994) and 34 new applications (received on a first come, first served basis) are being processed.  The main focus has been on natural gas.  Long term player, Anglo Operations has been operating a five-spot pumping test in the Waterberg since 2004 and plans to start another shortly. In the main Karoo basin since the beginning of 2008, other exploration companies have drilled 20 exploration wells to test coal-bed methane potential. The pace of drilling is expected to pick up significantly before the end of the year.

 

For decades, the methane encountered in underground gold mining in the Free State and Evander gold fields has been regarded only as a hazard and it is still being blown to waste in large quantities. A number of companies are investigating if this “waste’ can be turned to commercial advantage, with associated environmental benefits.

 

A fresh look is also being taken into the occurrences of oil hosted in sandstones of the Ecca and Beaufort Group in a wide arc across the northern and north-eastern parts of the Great Karoo basin, to determine if new technology can be applied to producing these challenging deposits.

 

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