Underground CO2 storage ‘could cause small quakes’

Storing carbon dioxide (CO2) underground is likely to cause earthquakes that could release the gas back into the atmosphere, according to new research.

Carbon capture and storage (CCS) in empty oil and gas wells is seen as a key tactic in the reduction of greenhouse-gas emissions from the burning of fossil fuels.

But scientists from Stanford University in the US believe that injecting massive quantities of CO2 into the ground would likely produce small earthquakes similar to those caused by the injection of wastewater.

Carbon injection is unlikely to trigger large, destructive earthquakes, said Stanford geophysics professor Mark Zoback, co-author of a paper on the research in the journal Proceedings of the National Academy of Sciences (PNAS).

‘The implications are different if you’re trying to store carbon for thousands of years,’ he said in a statement.

If geophysical faults slip by just a few centimetres, it could allow stored CO2 to reach the surface, he argued, and carbon repositories need a leak rate of less than one per cent every 1,000 years to be effective. ‘The bar is much higher in this case.’

Stress in the Earth’s crust can cause earthquakes even in the middle of the planet’s tectonic plates if pressure begins to build up.

Zoback and his colleague, environmental Earth science professor Steven Gorelick, reviewed field measurements and laboratory studies of shear displacements like the ones thought to have been induced by injecting wastewater as part of shale-gas drilling operations in the US last year.

‘Almost all of our current climate-mitigation models assume CCS is going to be one of the primary tools we use,’ said Zoback. ‘What we’re saying is, not so fast.’

He said that there would continue to be a use for CCS at a small scale, in regions that are near both CO2-producing plants and ideal geologic formations.

‘But for the US and the world to be considering CCS, one of the potential solutions to the greenhouse-gas problem, it’s a very high-risk endeavour.

‘We need options that are practical, don’t cost literally trillions of dollars and aren’t vulnerable to moderate-size earthquakes.’

A recent report from the US National Research Council concluded that ‘continued research will be needed to examine the potential for induced seismicity in large-scale CCS projects’.