By Beth Mole
Pumping carbon dioxide into the bowels of the Earth seems like an appealing way to ditch the greenhouse gas. But such injections could trigger earthquakes, geophysicists report November 4 in the Proceedings of the National Academy of Sciences.
Petroleum companies already use CO2 injections to flush out underground oil. Now researchers have found that such gas injections into an oil field in northwestern Texas sparked dozens of small earthquakes.
“It’s inconceivable that the injection wells weren’t contributing to these earthquakes,” says study coauthor Cliff Frohlich of the University of Texas at Austin. The study provides some of the first evidence that gas injections may lead to earthquakes.
For decades, scientists and engineers have known that injecting some fluids such as waste from hydraulic fracturing, or fracking, can alter underground stresses and lead to moderate earthquakes. But scientists knew little about the effects of injecting gases such as CO2. (Both of these practices are distinct from fracking, which has not been associated with earthquakes.)
In recent years, some engineers have proposed using injections to trap greenhouse gases underground and slow climate change.
Frohlich and Wei Gan of the China University of Geosciences in Beijing found that between 2006 and 2011, more than 100 earthquakes occurred at or very close to injection sites at the Texas oil field, where a company had been pumping in large volumes of gas since 2004. Eighteen of the quakes were larger than magnitude 3, which is big enough to produce low rumbles.
Before the 2006 quakes, the area had been rumble free since 1983 when a petroleum company halted water injections that triggered earthquakes between 1975 and 1982.
Despite the link to quakes, Frohlich says the idea of storing greenhouse gases underground shouldn’t necessarily be dumped. “This doesn’t mean it’s hugely dangerous,” he says. “Like a lot of science, it raises questions.”
The researchers note that oil fields to the north and south of the study site also underwent gas injections but did not experience quakes.
“The really puzzling question is why some places and not others,” says seismologist Emily Brodsky of the University of California, Santa Cruz. Brodsky and Frohlich agree that scientists need more research to understand which combinations of geological conditions and engineering techniques set off earthquakes. Part of the difficulty, Brodsky adds, is that energy companies often keep private data on injection sites.
“As seismologists, we’re being asked to answer these questions but not always given the data to answer them,” she says.
