Tremors pause fracking again at Cuadrilla’s Lancashire shale gas site

Preston New Road cu Cuadrilla Resources

Cuadrilla’s Preston New Road site near Blackpool. Photo: Cuadrilla Resources

More earth tremors overnight were strong enough to stop fracking for a second time this month at Cuadrilla’s shale gas site at Preston New Road near Blackpool.

The company said the tremors followed pumping operations yesterday (Friday 23 August 2019).

A statement, issued at 12.30am this morning, said there had been a 1.05ML event at 11.22pm yesterday.

A second statement, issued just after 6am, said a 0.53ML event had been detected at 5.01am.

Both statements said the tremors lasted “less than 1 second” and ground level vibration was about 0.4 mm/s.

Cuadrilla added:

“The integrity of the well has been confirmed.”

A smaller tremor, measuring 0.12ML at 10.41pm last night, was also reported by the company on its website.

At the time of writing, the British Geological Survey had confirmed one of the overnight tremors. It recorded the larger one at 1.1ML. The approximate depth was put at 3km, about 1km deeper than most of the previous seismic events at Preston New Road.

Earth tremors which happen after fracking has finished for the day are described as trailing events. Under Cuadrilla’s hydraulic fracturing plan for the PNR2 well, fracking must pause for 18 hours where the trailing event measures 0.5ML or above.

The company was required to pause fracking on PNR2 for the first time on Wednesday (21 August 2019) after a 1.55ML trailing event. This was the largest tremor so far recorded at Preston New Road. It was felt by people living in Blackpool, Lytham St Annes and villages near the site. A 1.0ML event on Thursday was also felt locally.

On its website, Cuadrilla said:

“Local people should be reassured that any resulting ground motion will be far below anything that could cause harm or damage and is likely to be much less than caused daily by other industries such as quarrying or construction or even heavy goods vehicles travelling on our roads.”

But a neighbour of the Preston New Road site told DrillOrDrop today:

“Given the number and intensity of the trailing events following Wednesday nights 1.55ML event, we are surprised the Cuadrilla and the Oil and Gas Authority thought it prudent to resume fracking so soon.

“With three more trailing events being reported overnight, we now wonder what the number and magnitude of earth tremors we can expect over this Bank Holiday weekend.”

Fracking began on PNR2 on 15 August 2019. Since then, there have been more than 80 seismic events. Three in the past four days have measured more than 1.0ML. So far, there have been red events, where earth tremors during fracking measure more than 0.5ML.

In autumn 2018, fracking of the first well, PNR1z, was paused several times by earth tremors.

During that operation, Cuadrilla called for the 0.5ML threshold to be raised.

89 replies »

      • Riley.

        [Edited by moderator]

        Your answer re Irish Sea is entirely unhelpful. I can only assume the answer is no, you have not investigated links between offshore o&g drilling and seismic events off the Fylde coast. And we all know the BGS has only recently split its events listings.

        [Edited by moderator]

        • Alan, I am also a Bristol Graduate too. So I must be terribly conflicted with referring to James Verdon’s work? Of course you will never know how many times I have advised industry (& governments) not to do things, that subsequently went very wrong. Or the times that I have investigated when industry has got things wrong, without my involvement, at great cost & in one case loss of lives. I am a scientist & I give my opinion as I see it at the time, to whoever is genuinely asking for it.

      • Wow, that’s definitive then. All that page does is say that there is no clear evidence that this ws induced activity. Your answer clearly says no, you have not investigated links with the offshore acivity. This is classed as a natural event because the BGS has no facility to check whether this is induced or otherwise.

  1. Sorry I come late to this discussion. A Sunday morning walk along the shore of the Med, followed by fresh sardines for lunch, took priority.

    Firstly, I agree entirely with Professor Styles that ‘trailing’ events are a fiction. The concept should never have been part of the TLS.

    Dr Nick Riley [edited by moderator] refers to the recent paper by Huw Clarke of Cuadrilla and several Bristol University authors. This paper, far from being “useful” as Dr Riley claims, is a very poor piece of work.

    Clarke et al. make no mention of the fact that 97.5% of the fracks (as measured from the daily report maps) lie north of the lateral. This is a highly unusual asymmetry which deserves discussion.

    Fracking of PNR-1z stopped for a month, but Clarke et al. do not tell us the truth as to why it stopped. They state:
    “From 3 November, CRL paused the injection program in response to repeated M >0:5 events that had occurred during the previous week. The injection pause continued until 7 December.”
    This is mendacious; the fact is that fracking had to be suspended because two frack sleeves had become jammed, and subsequently during the attempt to cement them and drill through, components got dropped off the drill string. These orphan pieces had to be pushed along to the end of the borehole and dumped (see my blog of 26 March 2019,, describing this). Pure technical incompetence by Cuadrilla!

    The paper purports to identify a ‘fault plane’ (called NEF-1) running ENE-WSW in the fracked zone north of the PNR-1z lateral. Six fault plane solutions (‘beach balls’) supposedly corroborate the existence of this fault. But the elongation of the cloud of events used to define this plane (by a least-squares fit process, and a very poor fit at that) is an artefact of the events forming a zone occupying a roughly ENE-WSW azimuth, this in turn being due to the fact that fracking occurred along a nearly E-W line.

    As all first-year earth science students learn (or did at least when I taught at Glasgow University) the ‘beach balls’ yield two possible solutions, mutually orthogonal. So Clarke et al.’s fault plane solutions can equally well be ascribed to separate faults trending NNW-SSE to NW-SE. This trend should be preferred a priori because the progression fracks mostly ran in that trend.

    Last, but not least, my mapping of many small faults in the zone between the two laterals PNR-1z and PNR-2 using the 3D seismic data volume shows several faults with N-S to NW-SE azimuths. One of these faults (P106) is vertical, trends NNW-SSE and corresponds well (to within 30 m) to the westernmost ‘beach ball’. The magnitude 2.1 event of last night lies close to my N-S fault P105, which dips east, but because the depth of the event is only listed approximately as 2 km, it might correspond better to displacement on one of two other nearby faults that I have mapped. Note that Cuadrilla has not recognised any of these faults.

    The EA and the OGA are both currently under threat of legal challenge because they approved the Hydraulic Fracture Plan for PNR-2 when they should not have done so. We shall see how that prospective legal action transpires in due course.

    • Thanks Prof Smythe. Finally some news of the pending legal action. No one on DOD seemed to know anything about this. Why is it taking so long? Surely an injunction to stop the stimulation of well 2 starting was the best legal option? Uder threat? Seems a bit pointless now?

      • [Edited by moderator]

        I also don’t see why you seem incapable of making a comment without trying to paint Cuadrilla as being incompetent at every opportunity. [edited by moderator] Why is it relevant to the paper written by Huw that after fracking was suspended due to a 0.5 Ml that no further fracking occurred for a month. They might have simply taken the opportunity to improve their well – big deal.

        The simple fact is that the downhole environment is harsh. Wells get distorted, tools get stuck – that’s the environment that in which all oil and gas companies work and there is no evidence that Cuadrilla are better or worse than any other company regarding their drilling and completion practices. Indeed, as the wells were completed and tested by service companies that work across the industry there seems no reason to blame Cuadrilla for those issues. One might argue that choosing the state-of-the-art completion design instead of the standard plug and perf was the reason for the sleeves getting stuck. However, the extra flexibility that the design has given may well prove very beneficial particularly with respect to allowing them to go back and refrac intervals into which insufficient proppent was placed.

        I’m not particularly sure what point you are trying to make about the subsurface interpretations. However, as someone who has been connected with this great industry for many years, I can be sure of one thing – the interpretation that you and Cuadrilla have made will prove to be wrong. In previous discussions, you clearly overestimate the accuracy of 3D seismic in positioning the lateral position of faults. The fact is that there are very large inaccuracies in the determination of the position of faults in the X-Y plane, which means that one cannot realistically use seismic in the way that you suggest to avoid fracking near small faults. You would be far better using tools such as the sonic scanner, which can measure the position of faults and fractures accurately in the borehole using reflections and assess the extent that they penetrate the formation using the frequency content of the Stoneley wave. Either way, the fact is that one is never going to identify all small scale faults that are likely to result in seismicity. The approach that Cuadrilla have taken seems sound. They have installed an amazing monitoring array, which you actually objected to for some reason. They are patiently testing the Bowland and the only thing that people can really whine about is that they have caused a few tremors that have created a surface ground motion less that what a train would do at 200 distance.

        [Edited by moderator]

  2. David, Are you going to publish your interpretations in a peer reviewed journal, perhaps in the same journal as Clarke et al. 2019, as a reply or discussion of their paper?

    • Yes Dr Riley. A comment for Seismological Research Letters is in preparation, with Prof Stuart Haszeldine (Edinburgh Uni) as co-author. But we are both snowed under with stuff to write up, not least about the other swarm of earthquakes at Newdigate (Surrey).

          • [Edited by moderator]

            it is important for scientists to put their opinions, interpretations out into the public domain ultimately via peer review. There is too much grey literature in the fracking debate, especially from those who contradict authors who have done the right thing & published via peer review, in reputable professional journals.

  3. Perhaps [Professor] Smythe’s claims have already been rejected by serious scientists Nick Riley, as previous claims have been. See

    [Edited by moderator]

    It seems that the concerns about the Newdigate earthquake ‘swarm’ being induced are fanciful. Rather than being induced by minimal injection a long way away, and at a different depth, it seems to join the long list of natural small earthquake swarms. Perhaps Prof Smythe could avoid wasting time with his fanciful claims that do not appear to have any credence with real experts. [ Edited by moderator]

  4. I shall ignore the usual ad hominem comments from the pro-fracking fraternity who have no qualifications whatsoever in conventional or unconventional hydrocarbon exploration (I except Dr Riley from this group).

    Let me give a taster of what I have found so far in the excellent Cuadrilla 3D dataset:

    1. The Wakepark Fault, running (coincidentally) from near Anna’s Road-1 to Preese Hall-1; one of the two or three most important faults in the Fylde. First identified by British Gas at depth in 1991, but totally absent from the Cuadrilla maps of nearly 30 years later. Curious, because it comes to outcrop above the toes of PNR-1z and PNR-2. The EA finally now (August 2019) accepts that it exists.

    2. Total absence of Millstone Grit above these laterals, this absence being proven by PNR-1 last year.

    3. Explanation for the total absence of MG at PNR (but present at PH-1) – large components of strike-slip movement on major faults cutting the Carboniferous.

    4. The Woodsfold Fault in the east, beloved by the EA as the magic barrier between the unconfined Sherwood aquifer (east) and confined aquifer (Fylde) comprises two separate faults. Running south, the northern strand turns into an E-W trend south of Kirkham, and it intersects the separate southern strand at right-angles in a complex geometry.

    5. An angular unconformity either within the Upper Bowland or at the Upper/Lower boundary, missed by Cuadrilla and the BGS.[Dr Riley, does that interest you, as the acknowledged expert on the Bowland?]

    6. Location of some of the PNR-1z triggered events on faults trending N-S or NW-SE as I mentioned earlier (the ENE-WSW NEF-1 fault is a fiction).

    7. A structural explanation for the extreme asymmetry of the PNR-1z microseismic activity; this asymmetry goes unmentioned by Clarke and co-authors.

    8. Various breaks in the continuity of the Manchester Marl, the supposed barrier to flow above the Bowland, in the PNR vicinity.

    9. More borehole evidence of fresh water originating in the confined Sherwood at shallow depth below the Fylde (so much for the EA writing off the whole of the aquifer as being entirely saline). Incidentally I have always accepted that the Wakepark Lake may be fed from Quaternary deposits – I consider that my suggested alternative, feeding from the Wakepark Fault, is just a possibility. Analysis of the water, including age-dating (which the EA has not done) would settle the matter.

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