Finally we have it – a proof that establishes that hydraulic fracturing carried out in oil and gas operations is directly responsible for small-to-moderate earthquakes.
For a long time the scientific community has believed that there is a link between fracking and earthquakes, authors of the study published in journal Science note. However, there have been no conclusive evidence that could answer the questions of how and why is seismicity induced by hydraulic fracturing. This changes now with the study by scientists at University of Calgary revealing the link that establishes the relation between fracking and earthquakes.
For their study, scientists at the university collected and analyzed seismic data going back to the winter of 2015, when the first seismic event exceeding magnitude 4 on the Richter scale, occurred in the Fox Creek area. To get the data they required, scientists resorted to information from private and public seismograph stations in the area and also a comprehensive database of hydraulic fracturing data from each well in the area.
Once the data that was required was at their disposal, scientists used advanced techniques to create a database of 905 distinct events. While the number of events was large, one thing to point out was that most of these events were too small to be part of existing seismicity catalogues. But, scientists were able to link seismic events to specific operations at individual wells, thanks to Repsol Oil and Gas Canada Inc. and Canadian Discovery Ltd., which provided data for the study. This university-industry partnership is crucial for researchers to gain access to data and to understand the fundamental processes.
Scientists were able to show a pre-existing but previously undetected fault system running parallel to two horizontally drilled wells. In one strand of the fault, hydraulic fracturing in both wells triggered small earthquakes by imposing mechanical stresses on the rock formations beneath the hydrocarbons-bearing zone — causing the fault to slip. In this case, movement on the fault effectively terminated when hydraulic fracturing operations ceased, consistent with existing regulatory protocols to halt operations under certain conditions.
However, in another strand of the fault — and more than two weeks after hydraulic fracturing injections had stopped — the magnitude 3.9 earthquake occurred at a calculated depth of just over four kilometres. This places the event within the upper levels of Precambrian basement rocks. Subsequent smaller seismic events persisted for a few months afterward, as the seismic activity migrated slowly from the basement back up toward the injection zone.
The researchers’ findings indicate that this persistent activity appears to be associated with infiltration of fracturing fluids into one strand of the fault.