On Shaky Ground

Storing large amounts of carbon dioxide underground will likely trigger small earthquakes, which could weaken the seal holding in the gas, according to a perspective article in Proceedings of the National Academy of Sciences.

Proponents of carbon capture and storage (CCS) hope to combat climate change by injecting carbon dioxide emitted from power plants into underground reservoirs. But to make a decent dent in greenhouse gas levels, the world will need to store about 3.5 billion tons of CO2 annually. And for carbon storage to be as effective as renewable energy strategies, less than 1 percent of the gas can leak every thousand years.

The problem is that if CO2 is stored near an active fault, injection of the gas could trigger an earthquake, two Stanford University researchers argue. For example, wastewater injections in the US caused small earthquakes in 2011, including a magnitude 4.7 quake in Arkansas. Stress measurements at a West Virginia site suggest that if more than 1 percent of the CO2 produced by a nearby power plant is injected underground, the increase in pressure could be enough to make the faults slip.

The authors note that their main worry is “not that injection associated with CCS projects is likely to trigger large earthquakes,” but rather that “even small to moderate earthquakes threaten the seal integrity of a CO2 repository.” Managers choosing carbon storage sites can probably avoid major faults, but identifying smaller faults will be challenging.

Safe carbon storage isn’t impossible, as long as the site is carefully selected. But it’s not clear whether there are enough of these sites to store the massive amount of CO2 that would be needed to fight climate change. The bottom line: “large-scale CCS will be an extremely expensive and risky strategy for achieving significant reductions in greenhouse gas emissions,” the authors say. Roberta Kwok | 18 June 2012

Source: Zoback, M.D. and S.M. Gorelick. 2012. Earthquake triggering and large-scale geologic storage of carbon dioxide. Proceedings of the National Academy of Sciences doi: 10.1073/pnas.1202473109.

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