Concerned that the natural gas boom is despoiling the environment? Here’s something else to shake you up: Some scientists think a 5.7-magnitude earthquake that struck geologically placid Oklahoma in November 2011 may be linked to wastewater injected into an oil field two decades earlier. It’s the largest quake ever linked to hydraulic fracturing, or fracking, the technique behind America’s current gas production boom, and it has some disturbing implications for fracking’s long-term effects.
The first is that fracking seems to be triggering a lot more quakes. “Significant earthquakes are increasingly occurring within the continental interior of the United States,” wrote the authors of the paper published yesterday in the journal Geology (paywall). “Concurrently, the volume of fluid injected into the subsurface related to the production of unconventional resources continues to rise.” (“Unconventional resources” means gas and oil extracted through fracking.)
The scientists noted that earthquakes with a magnitude of 5.0 or greater are rare in the US east of the Rocky Mountains. But between 2008 and 2011 there was an 11-fold jump in such temblors compared to the preceding 11 years, with 66% of the quakes hitting in 2011 alone. A 2012 US Geological Survey (USGS) study found that in Oklahoma, there have been 25 earthquakes a year of magnitude 3.0 and above since 2009, as against an average of 1.2 a year in the previous half century.
A second implication is that the after-effects can last a long time. Most fracking-related temblors are small and occur within months of when a mixture of water and chemicals are injected at high pressure into wells to break up rock formations that contain natural gas or oil. But in the case of the Oklahoma quake, it took place 18 years after wastewater from oil drilling at Prague began to be pumped into depleted wells for storage in 1993. In November 2011, a 5.0 seismic shock hit the region followed by a 5.7-magnitude temblor and many aftershocks. The quake destroyed 14 homes and was felt 800 miles away.
Within hours of the first quake, researchers from the University of Oklahoma installed dozens of seismographs near the epicenter, giving the scientists and their colleagues at Columbia University’s Lamont-Doherty Earth Observatory and the USGS detailed, real-time data on the shocks that followed. “The researchers hypothesize that as wastewater replenished compartments once filled with oil, the pressure to keep the fluid going down had to be ratcheted up,” Columbia University said in a statement. “As pressure built up, a known fault—known to geologists as the Wilzetta fault—jumped.”
The size of the quake is also cause for concern, according to the researchers. “The risk of humans inducing large earthquakes from even small injection activities is probably higher” than once thought, author Geoffrey Abers, a Columbia University seismologist, said in a statement.
It’s worth noting that not all scientists are buying that hypothesis. The Oklahoma Geological Survey, a state agency, blamed the quake on Mother Nature. “The interpretation that best fits current data is that the Prague Earthquake Sequence was the result of natural causes,” the agency said in a statement.
So there may need to be more studies. But the news could fuel opposition to fracking, especially in earthquake-prone California where drillers are eager to tap the state’s vast reserves of shale oil. And if the results are borne out, we may be living with the aftershocks of fracking decades after today’s natural gas barons have retired to Florida.
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