Originally Posted: March 1, 2018
Recent studies on hydraulic fracturing suggest the technology is causing more earthquakes than expected and that it doesn’t take the injection of much fluid to trigger a tremor.
In addition, researchers warn that the industry’s increasing reliance on “supersized” fracking using massive volumes of fluid and sand in longer wells could increase seismic hazards across North America.
A recent analysis of 300 hydraulically fractured wells near Fox Creek, Alberta, found that a modest injection of 10,000 cubic metres (2.6 million gallons) can cause an earthquake in geological formations containing faults.
The larger the volume of fluids injected underground, the greater the number of earthquakes, the study found.
“The rate of earthquake scales with the rising volume of injected fluids in sensitive areas,” said Gail Atkinson, one of the paper’s co-authors and a University of Western Ontario professor who holds a research chair in the hazards from induced seismicity.
“The more fluid you inject, the higher the productivity rate of earthquakes. It is almost like a dial,” she said. “It implies that you can affect the rate of earthquakes by changing the injected volume.”
But volume doesn’t seem to have any effect on the size of an earthquake that fluid injection might trigger if it hits a fault. In fact, no one can predict or model the potential severity of a tremor caused by oil and gas activities.
In fracking operations, energy companies inject high volumes of highly pressurized fluid, sand and chemicals underground to force open cracks in rock formations. The chaotic fractures, propped open by sand, allow hydrocarbons to flow.
In recent years the volume and pressure used in fracking operations has doubled or tripled in both Canada and the U.S.
A typical fracking operation in the Duvernay formation, which includes the area analyzed in the study, will inject more than 80,000 cubic metres, or nearly 17.6 million gallons of fluid and sand.
In Texas, the volume of sand used to prop open cracks in shale formations to release hydrocarbons has increased from 1,360 tonnes per well to 6,800 tonnes. In Canada, use has tripled from 3,000 tonnes per well to 12,000 tonnes.
At the same time companies such as Devon and Encana are experimenting with “supersized” fracking operations called “cube development” in the Permian shale formation in the eastern U.S. and the Montney Basin in B.C.
These deploy more force, sand and fluid by simultaneously drilling up to 24 wells into multiple levels of a shale formation. The process involves injection of fluids over an area more than a kilometre deep and several kilometres wide, targeting multiple depths.
“The total fluid volume is probably going to be very high with these cube developments and that means the potential for triggering a number of earthquakes could be large if faults are active in the area,” warned Atkinson.
The Canadian study found a “a statistically-significant correlation” between earthquakes and well pads in Fox Creek “with larger cumulative injected volume.”
The injected fluid must contact a fault which “can be located anywhere” under the surface, said Atkinson.
Since 2013 hydraulic fracturing has triggered hundreds of earthquakes in one part of the Duvernay formation near Fox Creek. READ MORE