Image: Columbia Earth Institute
The most contentious debate over hydraulic fracturing is probably the one about earthquakes. That's saying a lot, because fracking—the art of pumping a chemical cocktail deep into the earth's crust to pave the way for oil or gas extraction—has given rise to no shortage of contentious debates. There's also the ones about groundwater contamination, methane flaring, economic development—the list goes on.
But the fracking quake question likely tops the list, and scientists are increasingly finding evidence of a link. There's long been suspicion that fracking spurred a handful of minor quakes across North America and Europe—between 2009 and 2012, unusual earthquakes hit Oklahoma, British Columbia, and the U.K. Regulators in each—with the exception of the U.S., naturally—were concerned that oil and gas extraction operations played a hand in the unusual tremors. In the U.K., the energy company Cuadrilla ceased fracking after earthquakes shook nearby Blackpool. In the U.S., after strange quakes hit the south, the fracking action only continued to expand.
Scientists have acknowledged the link between injection wells and seismic activity since the 1960s, when drilling outside of Denver was tied to a 4.8 tremor. Cuadrilla's own investigation determined that its fracking operation was "most likely" the cause of the Blackpool earthquakes. And now, a new paper has just been published about the American tremors in the science journal Geology. Its title sums up the findings: "Potentially induced earthquakes in Oklahoma, USA: Links between wastewater injection and the 2011 Mw 5.7." And yes, the scientists appear confident that the earthquake was manmade.
The geologists investigated the largest of 2011's inland earthquakes, the trembler in Prague, Oklahoma that registered a 5.7 on the Richter scale. That quake, Oklahoma's biggest ever, was felt in 17 states, as far as 800 miles away in Milwaukee. The cause has been determined not to be the fracking process itself, but wastewater injection, a technique used to fill old natural gas wells with fracking wastewater. It's also used to pump oil out of old wells in a process known as enhanced oil recovery, which was the case in this study.
The Columbia Earth Institute explains why this is relevant now: "The recent boom in U.S. energy production has produced massive amounts of wastewater. The water is used both in hydrofracking, which cracks open rocks to release natural gas, and in coaxing petroleum out of conventional oil wells."
With both fracking and enhanced oil recovery, "the brine and chemical-laced water has to be disposed of, often by injecting it back underground elsewhere, where it has the potential to trigger earthquakes. The water linked to the Prague quakes was a byproduct of oil extraction at one set of oil wells, and was pumped into another set of depleted oil wells targeted for waste storage."
While examining the Oklahoma quake, the scientists used "the aftershocks to illuminate the faults that ruptured in the sequence, and show that the tip of the initial rupture plane is within ∼200 m of active injection wells and within ∼1 km of the surface."
Interestingly, those active wells were initially drilled 18 years ago. Back in the 90s, they were sucked dry, and sealed off. But then, when the oil companies came back for more, they turned to waste-water injection. After the wastewater fluid was blasted into long-sealed underground compartments, the "net fluid volume increase" slowly "lowered effective stress on reservoir-bounding faults." Scientists think that this may be why the earthquake occurred nearly two decades after the first drill bit was dropped.
It also means that many years can lapse between the first wastewater injection—or perhaps, a fracking operation—and an earthquake. The authors stress this point: "Significantly, this case indicates that decades-long lags between the commencement of fluid injection and the onset of induced earthquakes are possible, and modifies our common criteria for fluid-induced events."
This changes the game, in other words. It means fracking's likely got a longer tail—and considering the number of fracking operations currently underway across the U.S. right now, that's potentially bad news for those who enjoy a seismically stable earth.
The authors note in their release that "in the last four years, the number of quakes in the middle of the United States jumped 11-fold from the three decades prior." Which makes sense. We're blasting exponentially more fluid underground in our renewed and frenzied quest for domestic oil and cheaper-than-coal natural gas. And it's been a few decades since the easy-to-drill stuff ran out, and companies turned to injection techniques to increase their yields.
For the most part, the quakes linked to wastewater injection are small, and those alleged to result from fracking itself even smaller. But the Praque event injured two people and caused some serious property damage. And the mere fact that we're messing with seismicity should give us some pause about our fossil-fueled gold rush, especially about how we're ditching all the wastewater its creating. If we don't, a few years from now, or even decade or two down the line, things might get a little rumbly around here.