Cuadrilla fracked seven times before record-breaking tremor – official logs

pnr 190826 uwtoc-2

Campaigners outside Cuadrilla’s shale gas site at Preston New Road near Blackpool after the UK’s biggest fracking-induced tremor, 26 August 2019. Photo: Used with the owner’s consent

Cuadrilla fracked just seven times at its Preston New Road site near Blackpool last month before inducing a record-breaking earth tremor.

DrillOrDrop has seen official logs of fracturing at the site which show Cuadrilla was using volumes of frack fluid and sand significantly below the maximum allowed. The rate of injection was also under the limit.

Despite this, the operation induced the UK’s strongest fracking-induced tremor.

The Oil & Gas Authority suspended fracking at Preston New Road on 26 August 2019 within hours of the 2.9ML tremor. This was felt across the Fylde district and reportedly damaged homes. Another five tremors were felt by people living near the site.

16% of stages fracked

The official logs, which summarise daily fracking operations on the PNR-2 well, show there were main fracks on 15, 16, 17, 19, 20, 21 and 23 August. The number of frack stages is less than 16% of what Cuadrilla planned.

According to the logs, which were sent daily by Cuadrilla to regulators, a mini-frack was also logged on 13 August, two days before the company announced the start of fracturing operations.

The logs show that the company fracked along the length of the well furthest from the pad, from stages 1-7. The hydraulic fracturing plan for PNR2 indicated that the company planned to frack 45 stages with a total of 47 sleeves.

Fracking and seismicity

The 2019 daily logs, unlike those issued in 2018, do not give the time of each frack. But we know Cuadrilla was restricted to fracking during the day and there were no reports of tremors measuring 0.5ML or above while fracking was taking place.

The first significant seismicity was during the fourth main frack, on stage 4, on 19 August. Two amber events, measuring 0.0 were recorded at 10.35am and 11.06am BST. There was another amber event the following day during fracking on stage 5, at 10.13am BST.

The next important seismic event, measuring 1.6ML and an intensity of 3, was in the evening on 21 August 2019. Another measuring 0.9ML followed later that night. The logs showed Cuadrilla had fracked stage 6 that day, using the largest volume of fluid in the series, though with a reduced volume of proppant.

The final frack, on stage 7, on 23 August used reduced volumes of both fluid and proppant and a lower injection rate. It was followed by a 1.1ML intensity 3 tremor that evening and tremors measuring 0.5ML and 2.1ML the next day.

We estimate the 2.9ML tremor happened about 62-72 hours after the final frack.

pnr-2 daily logs data

Data from the PNR-2 daily fracking logs. Refracktion and DrillOrDrop

7% of total fluid used

Cuadrilla used a total of 2,485m3 of frack fluid during the August 2019 fracks – about 7% of the maximum permitted if all stages had been injected with the full volume per stage of 765m3.

The logs show the average volume of frack fluid used in the August main fracks were higher than that used in the main fracks on the PNR-1 well in October-December 2018. DrillOrDrop report on 2018 logs

All but one frack during August 2019 used more than 300m3 of fluid. But even the frack with the largest volume, at 432m3 on 21 August 2019, used only 56% of the maximum allowed.

The total proppant used in the August 2019 fracks was 289.1 tonnes. This is about 8.6% of the total that would have been used if all stages had been fracked using the maximum 75 tonnes allowed.

The average amount of proppant used during the August fracks was also larger than the equivalent in 2018. But the largest amount, at 55 tonnes, used on each of the 17, 19 and 20 August 2019 fracks, was under 75% of the maximum allowed.

What became the final frack, on 23 August 2019, used just 18.6% of the maximum volume of fluid allowed and just under 5% of the permitted amount of proppant.

Injection rate below maximum

According to the logs, Cuadrilla also kept the maximum injection rate (in litres per second) within the limit of 106.25 l/s.

The rate recorded for six fracks was either 78 or 80 l/s. The final frack, on 23 August 2019, recorded 53 l/s, 50% of the maximum allowed.

Additives increased

The company also appeared to be making adjustments to the proportion of additives in the frack fluid.

The first five fracks used additives at 0.02%.

But this was raised to 0.05% on 21 August and 0.06% on 23 August 2019.

1% flowback

pnr-2 daily logs mini frack pressure chart

Injection chart for mini frack at Preston New Road on 13 August 2019.  Contains public sector information licensed under the Open Government Licence v3.0

The logs reveal that the August 2019 fracks had lower volumes of flowback than the 2018 operation at Preston New Road.

The recorded flowback totalled 31m3, 1.2% of the total injected. The average flowback per frack stage was just 4.42m3.

Unlike the 2018 logs, only one of the 2019 documents has a chart of pressures, including calculations of bottom hole pressure in the well.

The mini-frack, on 13 August 2019, did have a chart measuring pressure against time. This indicated that maximum bottom hole pressure approached 600 bars. Pressure data is expected to be available in reports released by the OGA six months after the end of fracking.

  • The August 2019 logs were released under the environmental information regulations. This article contains public sector information licensed under the Open Government Licence v3.0 with the data according to the open gov licence. DrillOrDrop acknowledges analysis by Refracktion

11 replies »

    • Would be a strange pension fund that included Cuadrilla! But, as per usual, must not let reality stop a silly comment.

    • Taken from Cuadrilla’s website way back when,

      ‘Members of Cuadrilla’s management team have each played leading roles in the drilling and/or hydraulic fracturing of more than 3,000 natural gas and oil wells across the world.’

      If they are supposedly the ones with the know how I wonder how Aurora intent to proceed to ensure large earthquakes don’t happen and wells don’t get damaged?

  1. I see the earth tremors around PNR are still ongoing with an another amber event in the early hours of yesterday morning.

  2. This is ironic – you couln’t make this up if you tried:

    “Sulphur hexafluoride, or SF6, is widely used in the electrical industry to prevent short circuits and accidents.

    But leaks of the little-known gas in the UK and the rest of the EU in 2017 were the equivalent of putting an extra 1.3 million cars on the road.

    Levels are rising as an unintended consequence of the green energy boom.”

    “It is 23,500 times more warming than carbon dioxide (CO2). “

  3. A tricky one the classification of the seismic events. Cuadrilla only adopt red and amber terminology when fracking. According to the hydraulic fracture plan, trailing events of only greater or equal to 0.5 warrant any delays and pause for thought and reflection. So they fracked on Friday 23rd after a trailing ‘amber level’ of 0.4 hours in the early hours of that Friday morning probably due to the frack on Wednesday 21st that probably caused the 1.6 quake later that Wednesday. What prudence! So the ensuing 2.1 and 2.9 quakes could have been due to fracking on 21st rather than on the 23rd or a combination of both. And the thought of raising levels when after three weeks there’s still appreciable seismicity?! And if a critically stressed major fault outside the operational zone fails a month from now due to this disturbance …?…

  4. The 1% flowback particularly attracted my attention. So 99% of the water, proppant, additives, and whatever else it picked up way down the hole at immense pressure and heat (plus whatever different elements that heady mixture may have cooked up) just disappeared somewhere else. Quite clearly, it was doing an effective job of lubricating existing faults and fissures. I’ve spend enough time working on old buildings to know how determined water can be in getting through the smallest of holes and creating invisible small problems that turn into major problems over time… and that’s without applying 8702 lb per square inch of pressure (600 bar) to it.

  5. Mike Potter, you raise a very important matter of great concern! Hopefully it will be picked up on by our more knowledgeable readers about these things and investigated. After all water poisoning in mature fracking locations was caused by exactly this issue and promoted figures over here claim ONLY around 50% of contaminated used fracking fluids escape into the local environment!

  6. Indeed Peter. If the fracking industry were to be established at scale in this country, it would appear that the govt, EA and other regulators and no doubt numerous commentators on this site are content, nay sanguine, about pumping circa 50% of many millions of gallons of contaminated water deep underground, with little idea of where it will be going or seeping to over time. Worse still if it turned out to be 99% of those millions of gallons. I’ve seen many examples of what happens when this occurs (and heard about several first hand), including the deliberately long drawn out David v Goliath court cases, large payouts and non disclosure agreements. Presumably not quite so easy in our densely populated country. But not to worry, there will be plenty of folk with lucrative backing to strenuously deny those facts.
    In this specific case, I find it worrying that Cuadrilla appear to have had so little idea of the subsurface geology that they had no control or knowledge of where this water was disappearing to – or was it just not that important, or merely bad luck?! Powerful pumps and crossed fingers at Cuadrilla HQ seems like a dangerous and somewhat gung ho prospect to me. Similarly crossed fingers at Govt, OGA and EA HQs?
    Then there’s the other matter of dealing with the contaminated water the DOES come back to the surface: The huge quantities, storage, significant distances to transport by road, establishing treatment facilities, the energy used for treatment, the carbon emissions from all of that, then the final disposal of highly saline water (plus, heaven forbid, accidental or deliberate leakage or spillage). That’s always assuming that waste water reinjection isn’t suddenly and mysteriously found to be ‘best available technique’, with all the seismic and contamination implications that would likely bring.

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