Carbon capture and storage (CCS) is a proposed route to mitigate fossil-fuel greenhouse gases' impact on Earth's atmosphere, oceans and climate.

In CCS, CO₂ is captured from fuel burning at the power station, and pumped back down into the very rocks that maybe once yielded that fuel.

Likely storage sites for CO₂ will be depleted gas and oil fields one to two km down, with many candidates in the old oil and gas fields of the North Sea.

A few test sites around the world suggest that CO₂ can indeed be returned to the deep Earth successfully, but attention has now turned to monitoring its behaviour at depth.

Checking that it stays locked within the porous rocks of any CCS repository is an important step in validating the method.

Prof Jon Gluyas of Durham University stressed, at the British Science Festival in Newcastle, the importance of monitoring CO₂ once buried, to ensure that it stays within the storage site and to chart any changes with time, and simply to ensure that the carbon capture is permanent.

"It will be captured from power stations and other industrial plants, compressed into liquid form, and injected deep beneath the Earth. The methods we have for monitoring at the moment are expensive and just a snapshot. It costs around £1m a go," he said.

The current cost of monitoring CCS repositories is a major hurdle to adopting the method. Existing technology uses expensive geophysical seismic imaging techniques, which would need to be continued and repeated long into the future.

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Source: by Simon Redfern Science reporter, BBC News, Newcastle, 13 September