Fracking wells should not go to 11. Instead, turning down the volume — that is, of water pumped underground to help retrieve oil and gas — may reduce the number of earthquakes related to hydraulic fracturing.
The amount of water pumped into fracking wells is the No. 1 factor related to earthquake occurrence at Fox Creek, a large oil and gas production site in central Canada, researchers report January 19 in Science. An injection of 10,000 cubic meters of fluid or more at a well appears to trigger a quake.
Fox Creek sits atop the Duvernay Formation, a sedimentary layer rich in oil and gas. Before December 2013, the area was earthquake-free. Since then, hundreds of earthquakes have shaken the region; most were below magnitude 4, but a magnitude 4.8 quake in 2016 temporarily shut down operations.
Previous investigations revealed that fracking well injections at the site were triggering earthquakes on an underlying fault system. But mysteries remained: For example, why didn’t the quakes didn’t start until almost three years after fracking activities began in 2010?
Ryan Schultz of the Alberta Geological Survey in Edmonton and his colleagues compared the timing and location of the earthquakes with fracking activity at 300 wells in the region.
An analysis of rates of injection, fluid pressure and fluid volume for the wells closest in proximity to the quakes revealed that, at this site, only volume was linked to the quakes. A previous study has linked the rate of wastewater disposal injections to seismic slip (SN: 7/11/15, p. 10).
As for the three-year delay, the authors say, fracking well injections tend to increase in volume over time as operations mature. So once the injection volumes reached that 10,000-cubic- meter threshold, the earthquakes began.
Although fracking near Fox Creek began in 2010, the region only began to get earthquakes (red circles) in late 2013. Researchers say that’s because the volumes of fluid pumped into the wells (vertical gray lines) were increasing over time. By late 2013, the total volume pumped into some close clusters of wells had reached at least 10,000 cubic meters (or 104 m3), triggering quakes. Most of the earthquakes were below magnitude 4, but a large quake in early 2016 temporarily stopped fracking operations.