Does Carbon Sequestration or Fracking Cause Manmade Earthquakes?

Aftermath of September 4th Earthquake in Canterbury NZ. Bridge Street, South Brighton, Christchurch. (Photo: Martin Luff / CC BY-SA 2.0)

Mother Nature isn’t the only force that can trigger earthquakes: so can humans. Two new studies examined whether gas and liquid injections related to energy development might cause tremors. Substances are pumped into the ground for both hydraulic fracturing (also known as “fracking”) to tap natural gas reserves and sequestering carbon dioxide captured from coal-burning power plants.

Overall, the greatest earthquake risk appears to come from storing liquids and gases underground, not the actual process of fracking.

In a study published Monday in the Proceedings of the National Academy of Sciences, researchers from Stanford University looked at the possibility of causing earthquakes through carbon sequestration. The scheme involves storing pressurized CO2 underground to lock up these climate change-inducing greenhouse gases spewed by coal-burning power plants. This method requires continuously injecting large quantities of the gas, which is trapped under impermeable layers of rock. The concern is that over time, the change in pore pressure near preexisting, potentially active faults could cause earthquakes. Increased pore pressure reduces resistance to fault slip- this essentially means that it increases the ability to slide and thus cause earthquakes.

This isn’t the only study about manmade earthquakes. Public concern about energy development projects helped spur the U.S. Department of Energy to ask the National Research Council to examine seismicity related to energy and oil and gas development. The NRC, which released its report last Friday, found that oil and gas activities, especially the storage of wastewater, could create noticeable earthquakes in surrounding areas. As with carbon sequestration, the industry disposes of wastewater from processes such as fracking by injecting it below ground. That said, the study concluded that the actual action of fracking doesn’t cause many, if any, noticeable quakes.

Wastewater injections, on the other hand, do.

Murray Hitzman, a professor of geology at the Colorado School of Mines involved with the NRC’s study, testified at a Senate committee meeting yesterday that discussed the findings. He said that the largest seismic events “are associated with projects that did not balance the large volumes of fluids injected into, or extracted from, the Earth.”
 
We can see his statement in practice. A string of 12 small earthquakes in northeastern Ohio was found to be caused by injecting wastewater for storage, a process which is banned in some states.

The NRC has known since the 1920s that pumping gas and fluids out of the ground has the potential to cause seismic activity. In the 1970s, U.S. government scientists successfully turned an earthquake “on” and “off” by injecting water deep underground (removing the water turned the earthquake “off”). However the phenomenon is only now gaining recognition. In the past few years, a string of small quakes in Arkansas, Ohio, Oklahoma, and Texas linked to energy development have made people stand up and take notice. So what do the findings mean for carbon sequestration, a main component of “clean coal”?

“Our principle concern is not the probability of triggering large earthquakes; large faults are required to produce large earthquakes…our concern is that even small to moderate sized earthquakes would threaten the seal integrity of the formations being used to store the CO2,” said Mark Zoback, a professor at the Department of Geophysics at Stanford University, at the Senate committee meeting. While not involved with the NRC’s study, he was one researcher of the study that examined carbon sequestration.

While both studies raise some worrisome findings, the NRC cautions that more research needs to be conducted and that more site monitoring is needed. One thing is certain, though: ‘Out of sight, out of mind’ can’t be our motto for discarding the byproducts of energy production.

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