After studying hundreds of thousands of hydraulic fracturing (fracking) operations, the practice was determined to have caused noticeable tremors at the surface in only three cases and was "not a significant" source of earthquakes, according to researchers at UK's Durham University.
However, the researchers said that their findings provided conclusive evidence that fracking may cause dormant seismic faults to become active.
"We have examined not just fracking-related occurrences, but all induced earthquakes -- that is, those caused by human activity -- since 1929," said Richard Davies, a petroleum geology and earth sciences professor. "It is worth bearing in mind that other industrial scale processes can trigger earthquakes including mining, filling reservoirs with water and the production of oil and gas. Even one of our 'cleanest' forms of energy, geothermal, has some form in this respect."
The study, titled "Induced Seismicity and the Hydraulic Fracturing of Low Permeability Sedimentary Rocks," said almost all of the cases where fracking caused seismic events were undetectable by anyone other than geoscientists.
Two of the three exceptions that also could be felt by the general public included a magnitude 3.8 earthquake in 2011 in the gassy Horn River Basin, and a magnitude 2.3 temblor that same year near Blackpool, in Lancashire, England (see Shale Daily, Aug. 31, 2012; Nov. 4, 2011).
It was unclear where the third incident occurred. The Horn River Basin incident "is at the lower end of the range that could be felt by people," Davies noted.
Davies added that seismic events from fracking are "low compared to other man-made triggers. Earthquakes caused by mining can range from a magnitude of 1.6 to 5.6, reservoir filling from 2.0 to 7.9, and waste disposal from 2.0 to 5.7.
"By comparison, most fracking-related events release a negligible amount of energy roughly equivalent to, or even less than, someone jumping off a ladder onto the floor."
In August 2012, the British Columbia Oil and Gas Commission said operators in the Horn River Basin should be allowed to continue their activities but should also conduct more monitoring and data collection, citing a series of minor tremblors in the region from April 2009 to November 2011.
Meanwhile, UK-based Cuadrilla Resources Ltd. announced in November 2011 that a report it had commissioned found that fracking at its Preese Hall-1 site was likely responsible for a pair of small earthquakes near Blackpool.
Two months earlier, Cuadrilla said it had discovered a natural gas shale field in the Bowland Basin in Lancashire, which may hold as much as 200 Tcf (see Shale Daily, Sept. 26, 2011). Initial testing indicated the basin may be five to 10 times thicker than the Marcellus Shale.
"So we have concluded that hydraulic fracturing is not a significant mechanism for inducing felt earthquakes," Davies said. "It is extremely unlikely that any of us will ever be able to feel an earthquake caused by fracking. But theoretically, it cannot be ruled out completely; we cannot see every fault underground and therefore cannot completely discount the possibility of the process causing a small felt earthquake."
Davies said oil and natural gas companies could prevent the possibility of inducing seismic activities by avoiding geologic faults.
Scientists have linked a dozen small earthquakes in the Barnett Shale in North Texas to wastewater injection wells that support natural gas drilling (see Shale Daily, Aug. 8, 2012). Similarly, an injection well in northeastern Ohio was shut down in early 2012 after a dozen small earthquakes in the region (see Shale Daily, March 12, 2012; Jan. 5, 2012). Arkansas banned disposal wells in a portion of the Fayetteville Shale after quake activity there (see Shale Daily, July 29, 2011; March 4, 2011).