Sea change

Scientists at Durham University are studying the detailed geological impact of storing CO₂ from fossil-fuel power stations in former North Sea oil and gas fields.

Richard Davies, director of Durham University's Centre for Research into Earth Energy Systems (CeREES), said his team will do field tests in the southern part of the North Sea where most of the depleted reserves are located. In addition, he said, they are considering developing software that simulates CO₂ being injected into the reserves.

'People are used to looking at oil and gas in reservoirs, and they have software that predicts how oil and gas will flow out of reservoirs, but no-one has developed software that predicts what happens when CO₂ is pumped in,' he said.

The process is reversed and unpredictable, added Davies. 'You're increasing the pressure in the reservoir rather than reducing it,' he said. 'What's that going to do to the rocks? The whole system will change.'

Durham recently launched the Carbon Storage Research Group, which will be led by a professor of carbon capture and storage and energy. The new professorship is a three-way partnership between CeREES, DONG Energy and Ikon Science.

In addition to looking at storing CO₂ in depleted oil and gas reserves, the team is also researching the idea of injecting CO₂ into aquifers (underground bodies of permeable rock capable of storing large amount of water), or possibly ageing oil fields.

The latter idea has already been used for about 10 years in Norwegian offshore fields to improve oil recovery. In certain offshore oil fields, Davies said, oil is particularly 'CO₂-rich' and therefore Norwegian teams have had to take the CO₂ and pump it back underground.

'It keeps the pressure up in the oil field,' he said. 'Normally you pump water into an oil field to keep the pressure up, but CO₂ is more effective at pushing the oil out effectively. It is two or three times more effective.'

The Durham team's proposal would differ from what the Norwegians already do in that instead of capturing CO₂ and injecting it at the point of source, they will be injecting CO₂ that has been piped in from the shore.

Leading developers estimate it could be 20 years before carbon capture and storage is fully developed on an industrial scale. Davies and others argue that timescale needs to be shortened dramatically if the effects of climate change are to be combated.

'In the past 30 years we've take carbon dioxide out of the Earth and release it at a very high rate,' he said. 'Now we need to put it back where it belongs — underground.'

Siobhan Wagner