The scientists investigated the suitability of nine depleted natural gas fields in North America, China and Europe. These fields, they write, represent ‘a natural analogue for assessing the geological storage of anthropogenic CO2 over millennial timescales’. By measuring the ratios of stable isotopes of CO2 and other gases, such as helium and neon, in the fields, they built up a picture of how the CO2 had behaved there in the past.

‘Formed by volcanic activity tens of thousands or millions of years ago, these gas fields would once have been filled with CO2, and are the perfect place to go and see what happened and how it behaved,’ said lead author Chris Ballentine, a geochemist from the University of Manchester.

The scientists found that, in the past, much of the gas was transformed into carbonate minerals or dissolved in underground water – both of which essentially lock the carbon away underground – or it was simply trapped by a sealed system of rocks. Pilot studies are under way in the North Sea to assess the potential for injecting CO2 deep underground, as this kind of technology is used widely by oil companies.

June 2009