Buried carbon could escape, study finds

Carbon dioxide pumped underground for storage may dissolve the rock around it and escape, a new US study has found, putting the future of carbon sequestration into question.

Researchers injected 1,600 tonnes of liquid CO2 into a saline aquifer in a depleted oil field in Texas. Their results, published in the journal Geology, showed surrounding minerals to dissolve under the acidifying influence of the liquid CO2.

This could lead to the eventual escape of carbon into the atmosphere, said Yousif Kharaka, a geochemist at the US geological service who led the research. The penetration of brine polluted with toxic chemicals into drinking water supplies was another concern.

Having rejected the Kyoto protocol, the US government is promoting carbon capture and storage as one of the technologies that can help curb the rise in global CO2. Extracting carbon from fossil fuel-burning and injecting it into disused oil fields not only diverts the gas from the atmosphere, but also forces the remaining oil reserves out of the ground.

The technology is still at the experimental stage and awaits the verdict of the European Commission, which is expected to put out a policy paper on the issue by the end of this year.

Europe’s biggest carbon storage project is the on-going joint UK-Norwegian initiative in the North Sea, ran by oil companies Statoil and Shell (see related story). No evidence of leakage has been found so
far at the site.

The new study has shown no evidence of CO2 actually leaking, only the weakening of the geological formations holding it in place. This could be counteracted by using physical barriers, experts have said.

But the implications of the research are wide-reaching, as it is deep saline aquifers like that investigated by the US team hold the most promise as CO2 reservoirs.

Goska Romanowicz

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