STORING CO2 IN BASALT ROCKS COULD LIMIT SEISMIC RISK, PAPER SAYS

Tamar Hallerman
GHG Monitor
3/29/13

Basalt rock formations could hold the key to permanently storing CO2 while minimizing the risk of induced seismicity, according to a pair of Yale researchers. In a report published in a recent edition of the journal Geophysical Research Letters, researchers from Yale’s Department of Geology and Geophysics argue that common reactive mafic rocks like basalt or peridotite have the ideal properties for safe CO2 storage and could also minimize the risk of inducing the microseismic events that sometimes occur during injection. When supercritical CO2 is injected into the mafic rocks, according to the paper, it leads to a chemical reaction that mineralizes the carbon, permanently trapping the substance while reducing fluid pressure and more evenly distributing the stress from injection, subsequently minimizing the risk of induced seismicity more than in other rocks. 

In an interview this week, head author Viktoriya Yarushina said that as long as the party injecting the CO2 into the mafic rocks keeps a moderate fluid pumping rate, the potential for seismic risk is lower than with other geologies. “While [inducing seismic events] might be true when you inject CO2 into some rocks like sedimentary rocks, sandstones and limestones, the situation changes when you inject into basalts, which are quite common in the earth,” Yarushina said. “We propose a model that explains that when you inject your fluid into basalt, the fluid will react with those rocks, and while reacting, it will decrease the fluid pressure inside the rock, and that’s what basically decreases the probability of seismic events.”

While the idea of injecting CO2 into basalts is not new, this is the first time the geology has been looked at in terms of the potential for inducing seismicity, Yarushina said. She said that with her research partner, David Bercovici also of Yale, she developed a conceptual model using a National Energy Technology Laboratory grant to study the effects of the carbonation reactions on local stress levels during CO2 injection. The model examined groups of individual grains of rocks. When they injected fluids into non-mafic rocks, the grains slid back and forth against one another, increasing fluid pressure and upping the risk for inducing seismic events, Yarushina said. “In the case of the basalts, the contact area between the rock grains would increase, making it more difficult for grains to slide along each other and induce earthquakes,” she said.

Papers Initiated CO2 Injection Concerns

Yarushina and Bercovici began looking at induced seismicity after a pair of papers brought the issue of the safety of CO2 injection into the national spotlight last June. A peer-reviewed National Research Council report concluded that CCS “may” have the potential to cause “significant” induced seismicity, but also clarified that CO2 storage operations to date have not triggered any felt seismic events. The other paper, written by a pair of Stanford geophysicists and published as a ‘perspectives’ piece in the journal Proceedings of the National Academy of Sciences, said there is a “high probability” that small to moderate-sized earthquakes will be triggered by the injection of large volumes of CO2 into the subsurface. The Senate Energy and Natural Resources Committee held a hearing on both reports in June, where lawmakers expressed concern about the reports’ findings and questioned whether Congress should continue funding large-scale demonstration projects. CCS proponents rushed to prepare rebuttals, particularly to the Stanford paper, arguing that CO2 injection is safe as long as project operators adhere to industry best practices for monitoring.