Green light for carbon burial
- 10:00 17 February 2007
- Phil McKenna
The idea of literally burying the carbon dioxide emissions problem - by storing the gas deep underground - got a double boost this week. On 10 February, an amendment to international law came into force that allows the greenhouse gas to be buried beneath the sea floor. At the same time, a new study counters one of the main fears over carbon burial - that the gas will simply leak out again, to boost future global warming.
Some companies have been experimenting with storage in undersea aquifers and porous rocks for more than a decade, but the law was unclear over whether carbon dioxide should be considered a pollutant, leaving companies open to accusations of illegal dumping.
Even with the new laws, burying carbon dioxide under the seabed is likely to remain controversial because of concerns that it will eventually leak out (New Scientist, 20 November 2006, p 6). However, a team of environmental engineers now claims that these worries are unfounded, and that natural reactions will lock away the carbon dioxide within aquifers for millennia.
Ruben Juanes at the Massachusetts Institute of Technology and his colleagues made a computer model of the movement of carbon dioxide injected into a layer of permeable rock saturated with salt water. The gas is less dense than brine and so starts to rise in a plume towards the rock surface, but the model shows that it will not continue moving. The brine clings to the insides of the rock pores, narrowing their diameter so that the plume of gas is pinched into small bubbles, which remain trapped within the pores (Water Resources Research, vol 42, p W12418).
"This is a permanent storage mechanism," says Juanes. "Carbon dioxide will stay underground indefinitely." Nevertheless, G�nter Pusch at Clausthal University of Technology in Germany believes that the gas may still leak. "If the rising plume hits a fault or fracture network, it can accelerate the upward migration," he says.
"This is a permanent storage mechanism. Carbon dioxide will stay underground indefinitely
If the gas does leak out into the oceans, a team led by Toste Tanhua at the University of Kiel in Germany has found that it will remain dissolved in seawater for longer than previously thought. This leads to increased acidity at greater depths, harming deep-water corals and marine life (Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.0606574104).
Juanes, however, is undeterred. "So long as the gas is injected deep enough underground, it is hard to imagine a major leak making it to the surface," he says. "Sequestration is by no means an answer to all problems, but it is an integral part of the solution."
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