FRACKING TREMORS ARE NOT “TINY EVENTS”: THEY INDICATE A “CRITICALLY STRESSED” GEOLOGY, SAYS PROFESSOR OF GEOPHYSICS
Cuadrilla temporarily halted fracking at its site in Lancashire after a tremor located near the toe of their lateral well triggered the Seismic Traffic Light system. The seismic activity – around 0.4 local magnitude – was detected on Tuesday afternoon whilst fracking operations were taking place.
Even though it was not felt at the surface, the tremor is classed as an Amber event as part of the UK government’s traffic light system in place for monitoring seismic events during shale gas operations.
These are designed to protect the wellbore from the type of damage experienced seven years ago when fracking at Preese Hall. Cuadrilla has previously dismissed a 0.3 Ml tremor on the basis that it did not occur while pumping.
Emeritus Professor of Geophysics, Professor David Smythe told Frack Free Lancashire today:
“While the tremors induced to date are tiny, nevertheless the traffic-light system of monitoring induced seismicity does state that if a magnitude 0.5 event (or greater) is triggered by fracking, then the injection of hydraulic fluid must stop. But even this scanty piece of legislation has been poorly drafted, since it appears to permit tremors occurring after the end of a period of injection to be discounted.
“Cuadrilla now appears to be arguing that only events triggered during fracking, defined as actual injection of fluid under high pressure, will be counted in the traffic-light system.
“Scientifically, Cuadrilla’s slice-and-dice approach to the overall fracking job in a well is untenable, because there is often a delay between the end of an injection stage and the onset of a triggered event caused by the injection.
“For example, the Cuadrilla-commissioned report into the earthquakes triggered by fracking of shale in the vertical Preese Hall-1 well notes that the two strongest tremors (of magnitudes 2.3 and 1.5) each occurred about 10 hours after the cessation of injection in stages 2 and 4 respectively.
“The injection fluid needs time to seep along a fault zone until such time as enough of the fault has thereby been lubricated. If the shale is critically stressed – that is, it is ready to crack – the fault will slip, causing the earthquake. Cuadrilla was forced to admit that these earthquakes were caused by fracking at Preese Hall-1, although initially it denied any link. Unfortunately for Cuadrilla, all the shale in the Bowland Basin seems to be critically stressed, so the problem won’t simply disappear.”
In a statement, Frack Free Lancashire said:
“Seismicity must be monitored closely around the clock if hydraulic fracturing is allowed to continue in spite of the cluster of tremors we have seen around the toe of Cuadrilla’s well.
“Local residents are rightly concerned by these events and the fact that the traffic light system has had to halt operation just a week into the process. The issue is not whether these events can be felt, but whether they could be precursors to similar events that occurred at Preese Hall in 2011, which led to Cuadrilla’s performance as a licencee being questioned by the then Energy Minister, Charles Hendry.”
The well integrity and safety of what happens underground is beyond anyone’s control, following a seismic event. This risky technology employed by an inexperienced operator is something residents will never support and our strong opposition will continue.”
In parliament this week, during the All-Party Parliamentary Group (APPG) for Shale Gas, Chair Lee Rowley MP stated that the government’s Traffic Light System may only be applicable to Lancashire and not at other sites across the country. And via a letterto Kevin Hollinrake MP from Energy Minister Claire Perry MP, she stated that she would look to relaxing the seismicity trigger levels by adjusting them “upwards”, presumably to benefit the fracking industry.
ENDS
NOTES TO EDITOR
- British Geological Survey Earthquakes Around the British Isles in The Last 50 Days.
- Small quakes at fracking sites may indicate bigger tremors to come, say Stanford scientists
- Professor Smythe is available for interviews. Please contact Claire Stephenson for information.