Fracking “not significant” in causing earthquakes: U.K. research

Research out of the United Kingdom that considered hundreds of thousands of hydraulic fracturing operations indicates these produced only a handful earthquakes that could be felt on the surface, but that the fracking process has the potential to reactivate dormant faults.

Fracking involves water or other fluids being injected at high pressure below the earth’s surface to crack shale rocks and release natural gas.

The U.K. study showed the process caused earth tremors felt on the surface in just three cases, notes a statement released last week by Durham University, which led the study.

Almost all of the resultant seismic activity was on such a small scale that it was undetectable other than by geoscientists, notes the study, Induced Seismicity and the Hydraulic Fracturing of Low Permeability Sedimentary Rocks, funded by Durham University and Keele University.

“Most fracking-related events release a negligible amount of energy,” Professor Richard Davies of Durham Energy Institute says in the statement. The largest of the three felt, fracking quakes – the 2011 incident in British Columbia’s Horn River Basin – had a magnitude of only 3.8, Davies reports. “That is at the lower end of the range that could be felt by people,” he adds.

Last August, the B.C. Oil and Gas Commission concluded that “the events observed within remote and isolated areas of the Horn River Basin between 2009 and 2011 were caused by fluid injection during hydraulic fracturing in proximity to pre-existing faults.”

In the latest U.K. research, “we have examined not just fracking-related occurrences, but all induced earthquakes – that is, those caused by human activity – since 1929,” says Davies.

“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,” he adds.

“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,” Davies reports.

Researchers conclude “hydraulic fracturing is not a significant mechanism for inducing felt earthquakes,” he notes. Pointing out that it is not possible to see every fault underground, however, researchers “cannot completely discount the possibility of the process causing a small felt earthquake.”

That said, the study “established beyond doubt that fracking has the potential to reactivate dormant faults,” Davies says. To help mitigate the possibility of a fracking-related felt earthquake, he recommends having the oil and gas industry avoid faults that are critically stressed and already near breaking point.

A statement from Keele University issued last April outlined the main points of report produced by an expert panel looking into two earthquakes near the U.K.’s Blackpool area during the spring of 2011.

The panel concluded fracking caused the felt earth tremors, but that based on decades of observation of mining-induced seismicity from similar rocks of similar ages, the maximum event generated is about magnitude 3, “which is usually not going to cause structural damage, although it may be felt.”

The panel made recommendations to control the process to avoid small magnitude events, including the following:

• a much more cautious hydrofracture process where less fluid is injected, it is depressurized immediately after the fracture forms, and it is not held at pressure in the well for long periods as this can lead to fluid percolating along natural fractures and perhaps stimulating adjacent faults; and
• detailed microseismic monitoring before, during and after the hydrofrac, allowing the fracture to be mapped and perhaps tuned, which means a threshold level can be set at which work must stop and assessment done.

The B.C. Oil and Gas Commission notes that it became aware of the anomalous, low-level seismic events in Horn River Basin – only one of which was ‘felt’ at the earth’s surface – after they were recorded by Natural Resources Canada (NRCan) near areas of oil and gas development. “None of the NRCan-reported events caused any injury, property damage or posed any risk to public safety or the environment,” the commission states.

Its report contains recommendations, including the call to submit microseismic reports; establish a notification and consultation procedure; study the relationship of hydraulic fracturing parameters on seismicity; and upgrade and improve B.C.’s seismograph grid and monitoring procedures.