The debate about the safety of hydraulic fracturing operations has been reignited by a recent report about induced seismicity resulting from oil and gas operations. The study entitled: Potential Injection-Induced Seismicity Associated with Oil & Gas Operations was produced by a group of American drilling states, seismologists, academics and industry experts, and concentrates on seismicity potentially induced by injection of fluids in Class
II disposal wells.
The report states that although public concern has focused on hydraulic fracturing as a major source of induced seismicity, scientific evidence suggests that hydraulic fracturing has a far lower potential to induce “felt” earthquakes than underground disposal.
Incidents of felt-level seismicity associated with hydraulic fracturing occur far less frequently than those associated with Class II disposal wells and typically have lower magnitudes than injection-induced seismicity. This is because, although the volume of fluid injected over the short term is typically higher than with a disposal well, the duration of the process is much shorter. Also, during hydraulic fracturing the wellbore typically is subdivided into stages, isolating subsequent intervals so that extended fault contact is not likely. This is why, if fracking does end up producing earth tremors, they tend to be very minor, described by geologists as “microseismic events”, rather than earthquakes that are felt on the surface. Only in isolated cases of fracturing operations – such as in the case of Cuadrilla’s operations near Blackpool, UK – fracturing has reactivated pre-existing faults resulting in larger tremors.
The study quoted the findings of the National Research Council (NRC) report, which stated that only a very small fraction of injection and extraction activities among the hundreds of thousands of energy development wells in the United States have induced seismicity at levels that are noticeable to the public.
Having said that, the risk does exist and there are several methods to mitigate that risk in oil and gas operations. One such method is to monitor pressures during hydraulic fracturing. Another approach is to use advanced modeling to evaluate possible seismicity. When induced seismicity is associated with hydraulic fracturing, shutting down the pumping may result in a steady decrease in the number and size of seismic events.
When it comes to regulation, the report lists examples of regulatory risk management approaches from Canada and the U.S. but stopped short of suggesting model regulations.
Ohio Oil & Gas Chief Rick Simmers, who co-chaired the group that issued the report, says the report serves mostly as a primer for states, providing up-to-date scientific and technical data, along with suggested approaches for detecting and managing earthquakes. Since each state’s laws and geography are unique, “a one-size-fits-all approach would not be an effective tool for state regulators,” the report said.
Rex Buchanan, interim director of the Kansas Geological Survey and co-chair of the working group, told AP that human-induced seismicity “is a complex issue where the base of knowledge is changing rapidly.”
“State regulatory agencies that deal with potential injection-induced seismicity should prepare to use tools, knowledge, and expertise – many of which are offered in this primer – to prepare for and respond to [any] occurrences,” he added.
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