Underground injection of wastewater produced by hydraulic fracturing and other energy technologies poses a higher risk of causing earthquakes that can be felt by people than the hydraulic fracturing process itself, according to a recent study by the National Research Council.
Carbon capture and storage (CCS) could potentially cause seismic events because significant volumes of fluids are injected underground over long periods of time. But because no large-scale projects are in operation, not enough information exists to understand the potential for these projects to cause earthquakes, according to the committee that wrote the report.
The study, sponsored by the U.S. Department of Energy, examines the potential for technologies involved in shale gas recovery, carbon capture and storage (CCS), geothermal energy production and conventional oil and gas development, to cause earthquakes.
The total balance of fluid introduced or removed underground was found to be the factor most directly correlated with induced earthquakes, the committee said. Because CCS and geothermal energy each involve net fluid injection or withdrawal, all could potentially cause earthquakes felt by people.
However, technologies designed to maintain a balance between the amounts of fluids injected and withdrawn, such as most geothermal and conventional oil and gas development, appear to produce fewer-induced seismic events than technologies that do not maintain fluid balance.
Hydraulic fracturing, which involves injecting a mix of water, sand and chemicals in short bursts at high pressure into deep underground wells, cracks the shale formation and allows gas to escape and flow up the well with wastewater. Injecting this water underground is one way in which wastewater is discarded.
"Although induced seismic events associated with these energy technologies have not resulted in loss of life or significant damage in the United States, some effects have been felt by local residents and have raised concern about additional seismic activity and its consequences in areas where energy development is ongoing or planned," the committee said.
While scientists understand the general mechanisms that cause seismic events, they cannot accurately predict the magnitude or occurrence of these earthquakes due to insufficient information about natural rock systems and lack of validated predictive models at specific energy development sites.
Debate has ensued in recent months as to whether shale gas exploration activity causes earthquake activity.
Earlier this year, the Ohio Department of Natural Resources (ODNR) issued new standards for the transportation and disposal of brine, a by-product of hydraulic fracturing after an investigation of geological information and well activity data indicated that a number of earthquakes in the Youngstown, Ohio area had been induced.
While geologists believe induced seismic activity is extremely rare, it can occur with the confluence of a series of specific circumstances, ODNR officials said.
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