Tests point to less Karoo shale gas
• Analysis of rock-core samples from drillings show smaller deposits than US estimates
There is almost 40 times less shale gas in the Karoo than previously thought, suggest scientists who helped analyse recent rock core samples from test drillings in the Karoo.
There is almost 40 times less shale gas in the Karoo than previously thought, scientists who helped analyse recent rock core samples from test drillings in the Karoo say.
Prof Michiel de Kock, a senior paleomagnetist and head of geology at the University of Johannesburg, said very little sign of shale gas had been found in the first, directly measured, test samples dug from various depths, suggesting that previous claims about huge deposits were “grossly inflated”.
In the latest issue of the South African Journal of Science published on Thursday, De Kock and fellow researchers said previous estimates suggested the Karoo could be home to up to 485-trillion cubic feet (Tcf) of shale gas, which would mean the country had the fourthlargest deposits in the world.
The US Energy Information Agency later downgraded this estimate to about 390 Tcf, the sixth-largest in the world.
But De Kock said these estimates also appear to be “highly inflated” and it is now more likely that the technically recoverable shale gas reserves are closer to 13 Tcf. While these estimates are quite small in comparison to other parts of the world, De Kock and his colleagues nevertheless suggest that the Karoo deposits may still be of commercial interest to large gas-fracking companies such as Shell.
Hydraulic fracturing (fracking) is a controversial technology pioneered in the US, to break apart underground shale rock using high-pressure water, sand and chemicals.
De Kock said further tests still needed to be done in several “sweet spot” areas targeted for exploration, but his research group believed the Karoo deposits were “overmature”.
While the region may have contained large volumes of shale gas in the past, they were overheated by underground heat sources. Most of the gas had since escaped or been transformed over time into a more solid form, such as bitumen.
Using the analogy of a piece of steak on a braai fire, De Kock said the Karoo deposits appear to have been overcooked.
“What petroleum geologists would look for, ideally, is a nice medium steak. If the organic matter is uncooked, hydrocarbons would not have formed. If not cooked enough, there would be oil generation, but no gas generation. If cooked too much, as appears to be the case in the Karoo, the gas also would be driven off.”
The latest study — sponsored by Shell, on behalf of the Department of Science and Technology and National Research Fund’s Centre of Excellence for Integrated Mineral and Energy Resource Analysis — involved researchers from the University of Johannesburg, the Council for Geoscience, University of Cape Town and University of Portsmouth.