Cuadrilla Frack Tremor Triggers 'Red Light'
UK shale gas explorer Cuadrilla has paused its hydraulic fracturing (fracking), following a small tremor.
It confirmed a “micro seismic event” of 0.76 magnitude just after 11.30am at its shale gas exploration site in Preston New Road, near Blackpool in northwest England.
Cuadrilla confirmed that it was fracturing at the time and that the tremor was classed as a 'red event' under the traffic light monitoring system regulated by the Oil and Gas Authority (OGA).
“Operations have now paused for the next 18 hours during which seismicity levels will continue to be measured. The British Geological Survey (BGS) records seismicity to one decimal place and therefore have recorded the event as 0.8ML (local magnitude),” said Cuadrilla.
The BGS has confirmed the tremor, and also told NGW this was the first time that a ‘red event’ – requiring fracking to be paused – had occurred since the OGA traffic light system was introduced in 2014. It noted that smaller ‘amber’ events of just below 0.5 magnitude had occurred in the past week at Cuadrilla’s site; during one of these Cuadrilla confirmed it paused fracking. Cuadrilla pointed out that its on-site seismic monitoring equipment had helped detect the tremors.
BGS notes that tremors are triangulated from three separate locations, and that these also help detect magnitude and depth. Its page of recent UK tremors can be accessed here, and shows the Oct.26 is the 17th slight tremor near Cuadrilla's site since the firm resumed fracking for the first time since 2011.
In the Netherlands there have been stronger tremors caused by gas drilling and depletion and BGS' counterpart KNMI differentiates on its site between 'induced' and natural tectonic tremors.
The BGS does not as yet, as tremors have been slight. However the micro-tremors centered on Blackpool are likely due to shale drilling. The BGS said that fracking started at Preston New Road October 15 and the first seismic event BGS detected in the area was on October 18 and "not unexpected since hydraulic fracturing is generally accompanied by microseismicity – very small earthquakes that are too small to be felt." (The very slightest, indeed, are expressed as negative magnitude numbers)
Cuadrilla said: “All the relevant regulators were informed without delay and we have verified that the well integrity is intact. As per the hydraulic fracture plan in place at Preston New Road, work will now pause for at least 18 hours and is expected to recommence in the morning – Saturday, October 27, 2018.”
The OGA issued a statement saying it was aware of recent tremors near Preston New Rd, "including one of magnitude 0.76 today at an approximate depth of 2 km. Early indications are that these seismic events may have been induced by hydraulic fracturing operations at the site. The operator has paused operations to allow for more analysis to be carried out. The OGA is continuously monitoring operations to ensure they remain in accordance with the operator’s Hydraulic Fracture Plan (HFP), this includes: suspension of pumping/injection activities for 18 hours; reducing well pressure; continuing to monitor seismicity during the pause in injection operations."
Graphic showing the 'traffic light system' regulating onshore oil and gas activity (Credit: UK government)