Lancashire fracking tremors could reach 3.1 magnitude – but very unlikely, says Cuadrilla

PNR 181026 Ros Wills

Fence artwork outside Cuadrilla’s shale gas site at Preston New Road, 26 October 2018. Photo: Ros Wills

The maximum strength of tremors induced by new fracking at Cuadrilla’s Preston New Road site has been estimated at 3.1ML, the company said in a document published today.

The figure came in the hydraulic fracturing plan for the second well at the shale gas site near Blackpool.

Cuadrilla fracked the first well at the site, PNR1Z, in autumn 2018, inducing more than small 50 seismic events.

In the fracking plan for the second well, PNR2, the company said:

“Cuadrilla is anticipating that the horizontal well bore, or the area intended to be hydraulically stimulated, will encounter a number of small local faults.

“Modelling a conservative assumption … the upper bound estimate for maximum magnitude possible would be 3.1 ML, which is considered to be a very low likelihood.”

This level of earth tremor would be significantly higher than any induced by fracking at PNR1Z.

Then, the strongest was 1.5ML (DrillOrDrop tremor tracker). Cuadrilla said there were six tremors with a magnitude of 0.5ML or more – the limit under the traffic light system regulations at which fracking should pause for 18 hours.

Cuadrilla has repeatedly called on the government to raise this threshold. It has pointed to limits of up to 4.5ML used in a few other countries. So far, ministers have declined to review the regulations.

Today’s plan said the 3.1ML maximum for PNR2 was based on worst case scenarios. They included direct injection into critically-stressed faults and using 2,000m3 injection stages. The plan said not all faults were critically stressed. The company also intended to use less than half the modelled volume of hydraulic fracturing fluid per stage.

A previous version of the hydraulic fracturing plan for PNR2 was written in August 2018 but was withdrawn by Cuadrilla. Today’s version is 12 pages longer and has some changes. It will now be reviewed by the Environment Agency and the Oil and Gas Authority.

New procedures

The new version has changes to the procedures for responding to seismic events induced by fracking.

The previous plan required operations to verify well integrity after a trailing event – a tremor measuring 0.5ML or more that happened when fracking was not taking place.

190617 PNR2 fracking plan 3

Extract from previous version of Cuadrilla’s hydraulic fracturing plan for PNR2

In the revised version, operations can continue as normal if the centre of the tremor is outside the operational boundary. If it is inside, the operator must reduce well pressure, pause fracking for 18 hours and then verify well integrity.

190617 PNR2 fracking plan 2

Extract from revised version of Cuadrilla’s hydraulic fracturing plan for PNR2

Cuadrilla has also developed a ground motion prediction model in this version of the plan. This converts the magnitude of a seismic event at its origin into a predicted disturbance at the surface.

The plan said fluid volumes, rates, pressures and injection points would be adjusted if surface vibration caused by fracking was higher than 15mm/s PPV (peak particle velocity).

Other changes

Modelling for the revised version takes into account higher viscosity frac fluid, which Cuadrilla is seeking permission to use at the site. The revised plan includes gel fluids as an additive in the fracking fluid. The previous version referred only to polyacrylamide.

There is also extra information about geological features. Cuadrilla said:

“The empirical evidence derived by microseismic observations of activated geological structures confirms that unidentified critically stressed local faults are present and are likely to slip.”

190617 PNR2 fracking plan 1

Map of faults near PNR2. Extract from hydraulic fracturing plan for PNR2, 17 June 2019.

The company said five known faults (called Thistleton, Anna’s Road, PNR-1, SD3 and SD6) showed no activation during fracking of PNR1z. But a sixth fault, SD5, did show microseismic activity. This, however, did not lead to activity beyond the permit boundary, or any adverse seismicity, Cuadrilla said.

Reporting requirements have also changed. In the revised version, Cuadrilla said seismic events during fracking that measured above 0.0ML would be reported “as soon as possible” to the Oil & Gas Authority, Environment Agency and Health and Safety Executive. These regulators would receive a daily morning report during fracking operations only. The previous version said reports on the traffic light system status would “be reported in a timely manner” on Cuadrilla’s e-portal.

Fracking numbers

The plan confirms that Cuadrilla still intends to frack up to 45 stages of the PNR2 well. It proposes to use 765m3 of hydraulic fracturing fluid and 75 tonnes of proppant. The new version adds that there will be 47 sleeves used in fracking the well.

The company said it would take a “progressive stepped approach” using minifracs and “modest initial pumped volumes”, building up to the maximum pumped volumes.

Cuadrilla statement

Nick Mace, Cuadrilla environmental and permitting manager, said:

“We have already confirmed that both wells at our shale gas exploration site in Preston New Road, near Blackpool, Lancashire, remain candidates for hydraulic fracturing and each needs an approved hydraulic fracture plan in place before work can commence. This latest submission covers the second well.”


A spokesperson for Frack Free Lancashire said:

“We are disappointed to note that Cuadrilla have now published their latest fracking plan for Preston New Road.

“Considering they only managed to frack 5% of the first well and triggered 57 earth tremors, it is remarkable that they are pouring more resources into what we consider a doomed project.

“We also note that they now have permission to discharge into Carr Bridge Brook, against local wishes and representations.

“It seems extraordinary that, in spite of the recent declaration of a climate emergency, Cuadrilla are intent on continuing to explore for shale gas which we neither need nor want. This is completely incompatible with UK commitments on climate change.

“We will continue to campaign against fracking in particular and fossil fuels in general. This government should lead by example in transitioning to a cleaner and greener future.”

11 replies »

  1. What the BGS state in their review of the events at PH1

    ‘Nevertheless, 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’

    The 2.3M earthquake in 2011 gave enough cause for the Government to shut the industry down and now Cuadrilla propose a speculative 3.1M

    The magnitude scale is logarithmic. That means that if you add 1 to an earthquake’s magnitude, you multiply the shaking by 10.

    I wonder what house insurers, estate agents, Salwick nuclear plant, and BAE would say to these proposals?

    • I wonder what their ‘best case scenario’ and ‘average case scenario’ are?

      The 2.3M earthquake at Preese Hall 1 occurred after a 2,245 cubic metre injection into an adjacent fault zone.

      The BGS state

      ‘earthquakes in the magnitude range 2 to 3 ML require only relatively small rupture areas, and so can occur on small faults’

      Suggesting injecting multiple 2000 cubic metre volumes into critically stressed faults should hopefully make the Government see sense and place an instant permanent ban on any fracking proposals in Lancashire.

      • John – there are a few jobs going in geophysics at Aberdeen University – I’m sure they’d like someone with your great insight to apply

        • Yes I agree a great insight!!
          Googling non specific regions of the world which is not the UK, and great credibility with his friend Gayzer the clown Frackman. John what is your experience of the energy industry?, and do you, or do you not agree we have as a global economy doubled our consumption of Coal since the 70’s and that the current rate of renewable energy up-take, has not and probably will never in the long term keep up with the fossil fuel industry demand! I do believe that there is a transition period for energy exchange, but that fossil fuels is not going anywhere any time soon, neither is the UK addiction with Gas Supply and Demand!

          • I wonder how many of those damage reports were genuine – 2.4 Ml is generally too small to create significant damage. However, the shallow subsurface beneath Groningen could amplify ground motions, which isn’t likely to be the case in Lancashire. The landowners in Lancashire don’t have anything to be concerned about although I’m you’d like to make them believe that they do.

  2. Actually the Richter scale measures the amplitude from which a magnitude can be estimated. Adding one on the Richter scale does increase the amplitude by about 10 times, but the energy released (magnitude) is more than 30 times greater.

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