The potential for underground injections to cause earthquakes was thought to be a problem for natural gas, but a new National Research Council study says the impacted sector will not be gas. It’s a problem for coal.

Carbon capture and sequestration (CCS), pulling carbon out of emissions from coal-burning and storing it deep underground, has been prominent in clean energy planning over the last decade as a way to keep taking advantage of coal resources to meet energy demand while tackling climate change.

But the new study finds the large-scale CCS needed to keep using coal “may have the potential for causing significant induced seismicity,” study chair Murray Hitzman, professor at the Colorado School of Mines, told the Senate Energy and Natural Resources Committee June 19.

The study was requested by Committee Chairman Jeff Bingaman in 2010, who wanted a “comprehensive and independent study” of whether energy-related activities could inadvertently cause earthquakes.

They Felt the Earth Move

He made the request after small earthquakes were felt in areas of Oklahoma, Arkansas and Ohio that don’t normally experience quakes.

The quakes were allegedly caused in part by clusters of injection wells disposing of wastewater from industrial activities, including natural gas hydraulic fracturing. Fracking opponents have also claimed the process itself poses a seismic risk.

Bingaman asked the scientists to look at a range of energy activity, including fracking, geothermal wells, carbon dioxide injection for enhanced oil recovery (EOR), and carbon sequestration and storage (CSS) from coal burning.

Hitzman said the key factors for earthquake risk from underground injection are volumes and pressures.

Wells drilled for geothermal generation and for fracking turned out to be no problem as long as increases in underground pressures are relatively small and temporary, he said. The same was true for EOR, where the idea is to force out more oil and have pressures return to normal.

Susan Petty, President of Altarock Energy, said geothermal firms had experienced seismic problems in the past when wells were overpressured. Maintaining a pressure balance is key to long-term safe operation of geothermal resources, she told the committee.

Under Pressure

But CCS involves continuous injection of CO2 under high pressure for a long time and is intended as permanent storage, Hitzman said.

So is wastewater injection, but Hitzman said only a few of thousands of wastewater injection wells have been connected with quakes. Those generally involved higher pressures and volumes affecting previously undetected underground faults, he said.

“Energy projects with large net volumes of injected or extracted fluids over long periods of time, such as long-term waste water disposal wells and CCS, appear to have a higher potential for larger induced seismic events,” he said.

Stanford University Professor Mark Zoback said the oil and gas industry is increasingly avoiding the entire injection issue by recycling much of the water used in fracking.

But for CCS, he saw a slightly different problem than the study panel: induced small quakes that wouldn’t hurt people but would create cracks allowing CO2 to escape from underground reservoirs, negating their usefulness. He questioned how the world could find safe storage for the 7 to 8 billion tons of CO2 emitted now, let alone the 15 billion tons expected by 2050.

“The issue is whether the capacity exists for sufficient volumes of CO2 to be stored in geologic formations for it to have a beneficial effect on climate change,” he said, adding CCS “will be an extremely expensive and risky strategy.”

The witnesses did say more data is needed on baseline conditions, as well as better monitoring of injection effects, to minimize the potential for future energy activity to induce tremors.