Cuadrilla’s fracking site at Preston New Road, 24 October 2018. Photo: Eddie Thornton

Cuadrilla’s current fracking site in Lancashire passed a milestone on Friday.

A small earth tremor in the series that began 10 days ago near Blackpool exceeded the 0.5 magnitude threshold while fracking was underway. This triggered the first ever red light in the government’s regulations on induced seismicity.

The tremor, measured by British Geological Survey at 0.8, was too small to be felt at the surface. But under the traffic light system regulations it was enough to require Cuadrilla to stop work at its Preston New Road shale gas site for 18 hours and to report to the regulators on the integrity of the well.

Within hours of the tremor, Cuadrilla’s chief executive, Francis Egan, was telling the media that the red-light level in some other countries was 10,000 times higher than he was having to work to.

From a studio in Westminster on Friday evening, he said the 0.5 limit was “very challenging”. The limit in Canada was 4ML and companies in Europe were operating to red light levels of 2, he said.

In another BBC interview yesterday, he said:

“We are able to limit it to these tiny levels, but it’s very difficult to work within it.”

So how did the UK end up with a red light limit of 0.5ML for tremors induced by fracking?

For the origins of the 0.5ML limit, you have to go back seven years to the last time Cuadrilla tried fracking in the Blackpool area.

In the early hours of the morning of 1 April 2011, there was a small earthquake, measuring 2.3ML, felt across the  Fylde.

There were reports of toppled traffic lights and a cracked railway bridge. Residents waking in the night thought their homes were being burgled. Staff at Blackpool’s Bonny Street police station said they felt the building shake. It made the national news.

Preese Hall. Picture by Cuadrilla Resources

The earthquake was later linked to Cuadrilla’s fracking operations at the Preese Hall shale gas well. A Cuadrilla-commissioned report later in the year revealed there were 50 seismic events, including one measuring 1.5ML

The report described the seismic activity as “quite exceptional”. It said the 2.3ML earthquake was:

“2 orders of magnitude stronger than normally observed from hydraulic fracturing induced seismicity”.

The authors, Pater and Baisch, proposed a traffic light system and concluded that a threshold of 2.6ML during fracking at 3km deep would be a maximum acceptable magnitude.

But there was a complication in setting 2.6ML as the threshold at which fracking should pause.

The largest magnitude seismic events tend to occur after fracking has finished and the highest increase in magnitude after fracking was estimated at 0.9ML. So if your red light threshold was set 2.6ML during fracking, you could see a 3.5ML event after the injection operation had finished. And this would be beyond the 3ML worst-case.

The Cuadrilla report therefore recommended a red light figure of 1.7ML. This was based on the 2.6ML threshold minus the 0.9 maximum post-fracking increase in magnitude.

In 2012, a review of the Cuadrilla report for the then Department of Energy and Climate change (DECC), agreed that 3ML was a realistic upper limit for earthquakes induced by fracking. It also agreed that an earthquake of 2.6ML was unlikely to cause structural damage.

But this level of earthquake was larger than Preese Hall which, Pater and Baisch concluded, had led to deformation of the well. The DECC report authors, Green, Styles and Baptie, said of 2.6ML activity:

“Such an event would be strongly felt by people within a few kilometres from the epicenter and could cause some alarm.”

The review also rejected Cuadrilla’s proposed red light limit of 1.7ML. The authors said:

“We consider that the maximum magnitude threshold of 1.7 ML, initially proposed for the traffic light system, is undesirably high from the viewpoint of prudent conduct of future operations.”

They had looked at the pattern of activity preceding the Preese Hall earthquake on 1 April 2011 and all the seismic events had magnitudes below 1.7ML. So, if the threshold had been set at 1.7ML, the red light would not have been triggered at Preese Hall. There would not have been a pause in fracking before the 2.3ML earthquake happened.

The authors said:

“Based on this limit, no action would have been taken before the magnitude 2.3 ML event on 1 April 2011. Instead, we recommend a lower limit of 0.5 ML.”

In December 2012, the then energy secretary, Ed Davey, confirmed that the red level in the traffic light system would be set at 0.5ML. He described this level as:

“larger than the expected level generated by the fracturing of the rock”.

A document published online in 2017 by the Oil and Gas Authority described the 0.5ML level in very similar terms as

“greater than the level expected to be generated by the fracturing of the rock itself.

But this limit has already been passed in the first 12 days of operations at Preston New Road by one 0.8 tremor during fracking and one 0.8ML after fracking had finished yesterday. See DrillOrDrop tremor tracker

On the day fracking started at Preston New Road began, Francis Egan said he could “absolutely guarantee” there would not be another earthquake as a result of fracking for natural gas.

Yesterday, he said:

“You can’t create fractures in the ground without generating a seismic signature.”

Asked what level of tremor would worry him, he said:

“You have to get to a 2 at least before you can feel it.  You have to get to a 4 or a 5 before you get to any possibility of causing damage, not serious damage, so I’ll refer you back to the levels in other countries.”

But even before the 0.8ML tremor, critics of fracking were describing the rising magnitude of seismic events as “unacceptable”.

A spokesperson for the campaign network, Frack Free United, said the industry was in a ‘lose-lose’ situation:

“To continue risks a larger ‘industry wrecking event’, like Preese Hall 2.0. To stop just admits that they couldn’t see the fault before they started fracking.”

The local campaign group, Frack Free Lancashire, said:

“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 licensee being questioned by the then Energy Minister, Charles Hendry.”

Stuart Haszeldine, a professor of sedimentary geology at the University of Edinburgh, told the Guardian:

“The practical significance is not whether these tremors are felt at the surface or not, but in the potential to damage the borehole, and the potential to create gas pathways from the shale towards larger faults, towards shallower aquifers, and to the surface.”

So would the government raise the red light limit above 0.5ML? The OGA document from 2017 hinted that the limit could change:

“This level may be adjusted upward if actual experience shows this can be done without compromising the effectiveness of the controls.”

The energy minister, Claire Perry, used very similar words earlier this year in correspondence with the MP, Kevin Hollinrake (see DrillOrDrop report).

“The TLS [traffic light system] is set at an explicitly cautious level but, as we gain experience in applying these measures, the trigger levels can be adjusted upwards without compromising the effectiveness of the controls.”

But more recently, Ms Perry and another energy minister, Lord Henley, have said the government has no intention of changing the 0.5ML limit.

• Cuadrilla said yesterday it planned to resume fracking tomorrow (Monday 29 October) despite the 0.8ML seismic events on Friday 26 October and yesterday (Saturday 27 October 2018)