Earthquake risk undermines underground carbon storage as a viable strategy to fight climate change, say US researchers.
But an Australian expert in the technology says the conclusions are "scientifically untenable".
Professor Mark Zoback and Professor Steven Gorelick from Stanford University's School of Earth Sciences argue their case about carbon capture and storage (CCS) published this week in the Proceedings of the National Academy of Sciences.
"Large-scale CCS will be an extremely expensive and risky strategy for achieving significant reductions in greenhouse gas emissions," they write.
Governments around the world are supporting the development of large-scale CCS as a key weapon in the fight against climate change.
But, Zoback and Gorelick argue that the injection of large amounts of CO2 underground will increase the risk of earthquakes, which could lead to the release of the stored carbon.
While the general public may focus on earthquakes that occur at the edge of tectonic plates, 'intraplate' quakes also occur, in the interior of continents.
"The areas that we traditionally think of as stable still have high forces in them and those forces can occasionally produce naturally-occurring earthquakes," says Zoback.
He and Gorelick argue that there is a "high probability" that injection of large volumes of CO2 into such areas will also help trigger earthquakes.
"We know that over time earthquakes occur almost everywhere and we also know that sometimes building a dam and impounding water behind it is enough to trigger and earthquake and that's a very very small pressure perturbation indeed," says Zoback.
He says even a magnitude 4 earthquake that only produces light shaking could lead to leakage of carbon stored underground if it occurred on a small fault, missed in site characterisation studies.
"We don't think this is being considered enough,'" says Zoback.
He adds says pilot studies are not large enough to pick up such potential problems.
"If you inject a small volume for a short period of time you don't produce a large pressure change at depth. But when you inject large volumes of CO2 for many decades, you're affecting pressure over a much larger area."
Zoback says CCS could be useful in preventing release of CO2 from natural gas formations, which he describes as "very porous, permeable and compliant geological formations [that are] ideal for CCS".
"But we have to be very cautious before we talk about scaling it up to the level that is really contributing to greenhouse gas reductions on a global basis," he says.
"In that context the volume that has to be injected is so enormous that we are undoubtedly going to be use less than ideal geologic formations and in those formations we may very well have a serious earthquake problem."
But Australian carbon capture expert Dr John Kaldi rejects the study's conclusions that large-scale CCS will be an expensive and risky climate change strategy.
"That's the punch line but this final statement really is not supported by the rest of what I consider to be a carefully researched, well-documented paper," says Kaldi, who is Chief Scientist at the CO2 Cooperative Research Centre.
He criticises Zoback and Gorelick for making generic statements and not quantifying their conclusions about the risk and economic of CCS.
"Each site needs its own assessment. You can't make a blanket statement like that. It's scientifically untenable," says Kaldi, who is also, the chair of geosequestration at the University of Adelaide.
He says when experts consider a possible site for carbon capture they minimise earthquake risk by modelling what will happen when they inject the carbon dioxide.
"We can try to mitigate that risk by doing very careful site-specific assessments," says Kaldi.
He says if a risk at a particular site is found, the amount of CO2 to be injected can be decreased, or the location or orientation of a well can be changed, to avoid the negative impact.
"Yes there is a risk. There is a risk in everything we do. But what's the risk of not doing something like CCS?" says Kaldi.
And he says as a final safety net, monitoring of the storage will pick up any problems once CO2 has been injected so action can then be taken to reduce the pressure.
"You always have Plan B and Plan C in place for every storage site," says Kaldi.
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