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Carbon capture would create fizzy underground oceans

North Sea could turn to Perrier, cautions prof

By Lewis Page, 2 Apr 2009

New research has possibly given a boost to the idea of carbon capture, indicating that CO2 is sometimes held dissolved in underground water for millions of years. However, it is acknowledged that CO2 contained in subterranean water is prone to bubble out again, and often does so - famously at naturally-sparkling springs, for instance.

The new information comes from a novel carbon-sequestration study carried out by government-funded researchers in the UK and Canada. Rather than using computer modelling, the scientists examined nine gas fields in North America, China and Europe. They used isotopes of carbon and noble trace gases (helium, neon) as tracers to work out what had happened to CO2 naturally present in the ground many millennia in the past.

There are two theories as to what might happen to CO2 injected into old gas fields, as is called for by many carbon-sequestration schemes. It might be dissolved in water - "like bottled sparkling water", as the British government notes, using this as justification for the assertion that "carbon capture has a sparkling future".

The alternative thing that might happen to CO2 is that it might react with the rocks around it to form carbonate minerals. But, according to the Brit and Canadian boffins, this isn't much of a factor. They say that in seven of their gas fields, almost all the carbon went into water rather than rocks; in the remaining two, at least 82 per cent did.

Lead author on the study Stuart Gilfillan, who was doing his PhD at Manchester Uni during the research and is now employed at the Scottish Centre for Carbon Storage, plainly believes that the fizzy-water results offer an ironclad case that carbon storage underground will work.

"We already know that oil and gas have been stored safely in oil and gas fields over millions of years," he says.

"Our study clearly shows that the carbon dioxide has been stored naturally and safely in underground water in these fields."

The study is published as a letter to heavyweight boffinry journal Nature: subscribers can read it here.

But it may not be time to rejoice and fire up that new coal-fired power station just yet - or try to persuade the Chinese and Indians to stick capture kit on their rapidly-multiplying coal stations, as the Telegraph suggests.

Sequestration could turn the North Sea into Perrier

As anyone knows, after all, the CO2 in fizzy water is actually very prone indeed to getting out and escaping into the atmosphere. It would perhaps have been a better day for the idea of carbon capture if the stuff was being primarily stored as minerals.

In a commentary on the study, also published in the current Nature, Werner Aeschbach-Hertig of Heidelberg Uni takes that view, saying that the mineral carbonates are stable and offer the prospect of reliable storage over geological time scales - as opposed to fizzy water which often bubbles up to release its gas into the atmosphere, as for example in geysers, spas, French mineral-water sources etc. Lots of CO2 also comes out of wells and boreholes.

"Dissolution in groundwater implies the possibility of CO2 transport and eventual leakage to the atmosphere", cautions the German prof. In the case of Blighty, presumably stuffing our carbon into old offshore gas fields, we might start seeing the North Sea turning a bit bubbly.

Mineral carbonate as the primary mechanism might also have a downside, of course: many boffins think it would seriously limit the amount of carbon you could shove down an old gas well, as the formerly porous rocks through which the gas freely flowed would swiftly clog up with solid carbonate. But at least there'd be no real chance of the carbon simply popping up again somewhere else in the form of a spontaneous sea-bottom Perrier fountain.

Dr Gilfillan is naturally confident that carbon storage has a bright future, and reasonably points out that if an old gas field could hold onto its gas for thousands of years, it's reasonable to think it might hold onto fizzy water too.

The British government passionately wants this to be true, so as to start getting Blighty off its huge and swelling gas habit before the North Sea is totally played out, and to get the nation somewhere within striking distance of its promised carbon-cut figures. The projected scope for new British renewables and nuclear is nowhere near enough to achieve these things and keep the lights on too, so "clean coal" pretty much has to be real.

Even Dr Gilfillan hedges his bets, though: "carbon dioxide has been stored" is a far cry from "carbon dioxide can be stored in vast amounts without any getting out".

And the assembled researchers, in fact, merely say that mineral storage mechanisms can largely be ignored, and that future studies of carbon storage "should focus on the potential mobility of CO2 dissolved in water".

The jury's still out on carbon capture viability, then: and indeed, this research might well turn out to be an early nail its coffin, rather than proof of a "sparkling future" as would like to suggest. ®

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