Hydraulic fracturing may be in for a bumpy ride.
A previously unreported study out of the Oklahoma Geological Survey has found that hydraulic fracturing may have triggered a swarm of small earthquakes earlier this year in Oklahoma. The quakes, which struck on Jan. 18 in a rural area near Elmore City, peaked at magnitude 2.8 and caused no deaths or property damage.
The study, currently being prepared for peer review, follows news today that Cuadrilla Resources, a British shale gas developer, has found that it was "highly probable" its fracturing operations caused minor quakes of magnitude 2.3 and 1.5 in Lancashire, England (Greenwire, Nov. 2). The Cuadrilla study could complicate the expansion of hydraulic fracturing for shale gas in risk-averse Europe, where France has already banned the practice.
Fears of induced minor earthquakes have already complicated development of geothermal energy in regions like Nevada and Switzerland. Triggered earthquakes have also been tied to the long-standing American practice of injecting wastewater into wells. However, most geologists doubt that fracturing can muster similar seismic activity.
That is exactly what the Oklahoma seismologist who prepared the study, Austin Holland, told the resident reporting the quakes, who mentioned that fracturing had begun the day before at a nearby well. Earthquakes are typically triggered by stresses more prolonged than those found in fracturing, a reason it is generally held in the geology business to cause seismic events of magnitudes less than zero.
"These were just normal naturally occuring earthquakes," Holland told the resident.
But out of due diligence, Holland began examining the suite of almost 50 seismic events that followed the 2.8-magnitude quake. The majority of the microquakes struck within 3.5 kilometers of the fracturing well, Picket Unit B 4-18. The quakes were shallow and fit well in time and space with the start of fracturing in the nearby well. The geophysical model fit, too.
"The more and more we looked at it, it looked like it was a correlation," Holland said.
This is not the first time that fracturing has faced a possible link to earthquakes. The first case occurred in Oklahoma in 1978, featuring 70 microquakes in just over six hours, while a decade later, scientists linked fracturing to 90 small events. Both studies suffered from limited data, however, and their connections were far from definite.
With his arm twisted, Holland would still not definitively tie the microquakes to fracturing at the well. It is fiendishly difficult to attribute earthquakes, given existing scientific uncertainties about why and when quakes are triggered. What is clear is that the quakes are not common: As Holland noted, firms have drilled 100,000 fracturing wells in Oklahoma, with three minor seismic events reported.
The fracturing continued at the Picket well after the earthquakes, and the survey detected no additional seismic activity during that time, Holland said. The well was located in a geologically complex region riven by thrust rocks, he added, and a quake would likely have occurred at some point with or without the drilling -- the rocks were primed for it.
"These earthquakes were likely to happen," he said.
Holland's findings are likely to draw broad interest from groups opposed to fracturing, and he has already received queries from the industry about his work. Indeed, both the Cuadrilla study and Holland's report contain important lessons for the industry, said Chris Tucker, a spokesman for Energy in Depth, an oil and gas trade group.
"These reports from Oklahoma and the U.K. include a pretty good number of recommendations on how to avoid these issues in the future," Tucker said, "and so I'm sure they'll be something to which folks both here and abroad pay pretty close attention moving forward."
Reporter Mike Soraghan contributed.