Guest post: Fractured fracking ambitions

Stuart Haszeldine, Professor of Geology at the University of Edinburgh, reviews new research on fracking-induced earthquakes, released yesterday by the Oil & Gas Authority. The studies analysed hydraulic fracturing at Cuadrilla’s Preston New Road shale gas site near Blackpool and concluded that induced seismicity was difficult to predict and to manage.

Cuadrilla’s Preston New Road site near Blackpool, 20 August 2019. Photo: Ros Wills


The rocks which make up the upper earth, or colloquially the ground we live on, are in a fine balance of being pushed forwards, shoved sideways, pushed up, or loaded down. 

These movements are consequences of forces and loads sometimes imposed from hundreds of kilometres distance; but the effects of those forces are the stresses held in rocks for thousands, and even millions, of years.

Occasionally through geological time, those forces combine in a direction and a magnitude to fracture the rock. Or more commonly to reactivate movement along pre-existing fractures and faults. This is one way of producing earthquakes – which in the UK can sometimes be felt at the surface as ground movement. Very rarely in the UK, earthquakes release enough energy from the stored rock stresses to cause movement and damage at the surface. But much more frequently the earthquakes of lesser energy – hundreds of thousands every year – have no effect on surface dwellers and can only be detected instrumentally.

The purpose of high fluid-volume fracking is to artificially engineer injection of fluid into a borehole, such that the rock is quickly stressed during tens of minutes, to produce artificial fractures.

Inevitably the threshold of additional stress to create those induced fractures will be influenced by the stresses already held in the rock, and the location of fractures and movement will be influenced by pre-existing fracture locations and directions in the rock.

In the UK there are many thousands of pre-existing faults, and the complex ancient and recent geological history makes it extremely difficult to locate all the faults and fractures, and makes it almost impossible to accurately predict the stress imposed on each fracture or fault.

Thus, the effects of human intervention are hard to determine in advance, and even if an earthquake occurs, it can often be difficult to assign that effect to the cause of nearby human activity.

The HiQuake database (www. has compiled many of the earthquakes suspected of being linked to human activity and lists 1196 events since 1868, of which 33% are associated with fracking, whilst acknowledging that the smallest events are the least well reported.  For all these reasons, the association of earthquakes with stress caused by fracking is very contentious and will undoubtedly remain debated for years to come.

Lancashire shale gas

Preston New Road 1 and 2 wells, as well as Preese Hall also in Lancashire, are well known as deviated boreholes, where high volume fracking was attempted.

At Preese Hall in 2011, there is no doubt that fracking produced a small earthquake, which was recorded by seismometers, was felt locally, and reactivated a small fracture to move several centimetres – cutting through the borehole. 

PNR1Z well at Preston New Road Upper Bowland Shale

After five years of review, hydraulic fracturing operations were attempted by Cuadrilla Resources on the PNR1Z well at Preston New Road in autumn 2018.  Much more strict regulations were imposed by Government, meaning that fracking fluid water volumes were smaller and that fluid pressures during operations would be smaller. And a Traffic Light System was instigated, to halt work if tremors exceeded a pre-determined Magnitude.

The site was also instrumented a lot more intensively, because detection of small earth tremors, containing very little energy, needs to be close to the source. This is in a similar way to how humans hear sounds much louder close to the source, but the sound is fainter when distant from the source.

The information collected during those attempts at closely supervised fracking was released by Westminster government’s Department of Energy (BEIS) to its regulator, the Oil and Gas Authority (OGA).

During 2019, the OGA arranged for three different and independent scientific groups to undertake paid analyses of four different aspects of this information. These projects were continued to include analysis of additional information from PNR2 hydraulic fractures.

PNR2 well at Preston New Road, Upper Bowland Shale, 200m shallower than PNR1

This well was drilled, and then after PNR1 in 2018, was fractured during late 2019. The seismicity was closely monitored and pauses introduced after larger tremors, and the injection of fracking fluid limited to sub-economic volumes. Even with these precautions the fracking was terminated on 26 August 2019, after an earthquake of 2.9 ML.

Extract from British Geological Survey database of induced earthquakes

In March 2020, the OGA continued the four existing studies from PNR1 to include study of seismicity resulting from the PNR2 hydraulic fracturing operations. These are:

  1. Geo-mechanical properties of the rocks by Outer Limits Geophysics
  2. Compare the measured surface Magnitude ML with the recorded subsurface moment Magnitude Mw undertaken by the British Geological Survey (BGS)
  3. Intraseis Ltd to analyse and predict the surface impacts caused by ground motion following earth tremors or earthquakes
  4. BGS to investigate aftershock tremors following an individual triggered earthquake


The analysis and interpretation from both PNR1 and PNR2 boreholes has now been compiled and interpreted to provide conclusions.

These detailed studies were only possible because of the much larger data sets of measurement available. That followed specific regulatory requirements for these two boreholes which ensured surface and downhole microseismic measurements, coincident in time with operational datasets for fracking fluid pumping volumes, pressures and other borehole logging data such as 3D location of microfractures.

Even with these multiple and local instruments – several more than any other UK site – the interpretation is not at all simple, or predictive.

• The Geo-mechanics analysis concluded that multiple mechanisms exist which could cause the larger felt earthquakes, and no simple single cause could be identified.

• The Magnitude comparisons found that the two boreholes produced different results, so no simple prediction can be made of surface effects.

• The surface impacts study successfully modelled a 16x15km zone around a simulated earthquake.  Damage to 52 buildings occurred by comparing to the recorded 2.9ML event. Following an “unlikely” 4.5ML event, abundant damage to buildings would occur within a 1km radius with lesser damage within a 4km radius. In such a case, the borehole itself would not inevitably be damaged. [Although that assumes that no fault or facture intersected the borehole – as it did with Preece Hall]

• The aftershocks could not be predicted with certainty, although there is a correlation with volume of fracking fluid injected.

• The detailed 3-D tracking of fracture growth in real time from the borehole, induced by fracking, had no correlation between the two boreholes, even though those are closely spaced in similar rock units

• Fracking of PNR1 detected a previously unknown fault, which is not geographically oriented to slip easily in alignment with pre-existing stress in the rock

• Fracking of PNR2 also detected a previously unknown fault, which is well oriented to slip in the pre-existing stress in the rock – and this fault produced a 2.9ML event.

What does this mean?

These two boreholes have enabled the gathering of a huge quantity of detailed data during fracking and earthquakes. The cost of obtaining this data and its analysis was speculatively at least £ 10M per borehole. That is beyond normal budgets for government research funds. Unless new developers emerge who are willing to challenge the de facto bans or planning prejudice against fracking across the UK, it is unlikely that any more detailed scientific work on fracking and seismicity is planned in the UK. 

Even the abundant and detailed data from these two boreholes does not improve answers to the questions such as:

“does this borehole intersect a fault?” – both of the PNR boreholes discovered new faults

what is the limit a borehole frack pressure can reach?” – the two boreholes achieved very different fracture directions at different fluid pressures

“how will the first borehole influence subsequent boreholes?” – the second PNR borehole produced greater seismic effects than the first

Neither does this study provide significant data to help developers identify which parts of the UK may be better, or worse, suited to attempted development by fracking. 

The complexity of UK geology is a profound obstacle to precise geological appraisal of fracking developments, which must include:

  • technical excellence such as precise 3D mapping of faults
  • accurate stratigraphy of rock layering with fold and fault structure
  • excellent understanding of rock geomechanical properties, including residual stress direction and amount – rock layer by rock layer.

One OGA recommendation for any future instrumentation of fracking is that a denser network of (shallow borehole) sensors should be used to improve event detection, given the limited (in)completeness of surface catalogues in the UK. Geophone detectors (like microphones) need to be installed down shallow boreholes to detect small tremors. And a more abundant array of surface geophones is needed to detect larger earthquakes. Meaning that developers will need to work significantly harder.


A final conclusion derived from OGA’s funding of scientific analysis is that there are no simple results from these studies.

So, high quality prediction of earthquakes or tremors probability or magnitude resulting from fracking is not currently possible in this region.

Significant damage to surface buildings could result from an unlikely earthquake event, which it is not possible to exclude.

21 replies »

  1. Prof Haszeldine’s account is an excellent and concise summary of the irrefutable facts of geology.
    This is also entirely consistent with the advice, given several years ago, to local residents (and Lancashire County Council) by emeritus Prof. David Smythe:

    ” The geology of the US shale basins is fundamentally different from western Europe.
     The UK shale basins are heavily faulted, from the shale layer right to the surface, in contrast to
    those of the USA…
     …The current UK regulatory regime is ill-equipped to deal with this problem.
     Fracking for gas or oil should be banned in areas of complex faulted geology; in effect this
    means an overall ban in the UK.
     There will be no ‘shale gas revolution’ in the UK because in complex geology the production
    process is uneconomic.”

    Given these facts, it makes no sense for Cuadrilla to suggest that they may reapply for any future licence(s) to frack at PNR, Little Plumpton. Now is also the time for HM Government to upgrade the ‘moratorium’ to a formal permanent long-term ban on fracking in the UK.The site should be decommissioned and immediately restored to safe agricultural land.

  2. A very interesting read, highlighting the complexities and uncertainties for fracking in the U.K. Surely the fracking industry should accept it is time to call it a day? Time has moved on and the U.K. geology is complex, fracking is deeply unpopular with the public and local communities and as we move to net zero the emphasis is on less not more gas, plus the U.K. already has gas security of supply.

  3. Confirmation that fracking is inappropriate here, due to the adverse geology.

    The whole policy of cutting “the green crap” and going “all out for shale” has been a wasteful failure. It was always incompatible with climate heating and has set back innovation in renewables. As a result we now need even more urgent GHG cuts.

  4. Well, once again you have to add incorrect statements, KatT. Fracking is NOT deeply unpopular with the public. There are official stats. that show that statement is just FAKE. The survey shows it is unpopular with a MINORITY, and many of them admit to knowing little about the subject.

    So, why on earth should an “industry” take any note of your opinion when it is proposed in that way? I really would have thought you could find a means to make your point and still stick to what is correct/real.

    • Martin, my statement is not FAKE. Because anyone that can understand statistics can appreciate, as taken from the governments own survey in just May of this year, 45% opposition to fracking at the same time as “Support for fracking fell to a new record low of 8%. Just 1% of those surveyed strongly supported fracking.” supports my statement. And please do not resort to the FAKE argument that those surveyed sat on the fence means statistically anything other than that. Undecided means undecided. It does not mean they oppose fracking, it does not mean they support fracking. In addition survey statistics have repeatedly shown, the more people learn about fracking the more likely they are to oppose it.

      Whilst the government surveys may have fluctuated slightly, the trend has been one of far higher opposition compared to support. And I’m sure if the fracking moratorium was lifted the issue would become more high profile again, with continued strong opposition.

      Even a survey on behalf of the Conservative Environmental Network found that only ….

      “37% of conservative voters supported fracking, compared 74% who supported onshore wind.”

      And of course, if you surveyed communities threatened by fracking, it is likely that opposition would be even higher. I’m suspect that Lee Rowley would confirm that fracking is deeply unpopular in his constituency. No doubt you will accuse these communities of being NIMBYS but that is disingenuous as these communities support and oppose fracking in any location, not just their own and have fought a national campaign.

      Below I have provided some more evidence just to further support my point and purposefully didn’t quote from the Guardian because, you complained about that!

      I respect people that have a different opinion to me. But when opinions are put forward seldom backed up by evidence it is personal at best and when the opinion of others are challenged without evidence and at times the comments become personal it is nothing more than bigotry.

      • Oh yes it was FAKE, KatT!

        Interesting that you persist to prove your point even when your error has been pointed out. Not the first time, either.

        DoD reported on November 12th the results of the survey, for September.

        What did it show?

        36% of those surveyed opposed fracking. I repeat, 36%. If 100% is the total, then 36% is indeed a minority.

        So, you wander off into selected numbers of those who oppose and then try to muddy the waters with numbers who support-which has absolutely nothing to do with your original post. And then to add links to media as an excuse! Well, I can refer you to MANY media quotes that are ill informed and inaccurate, so they do not make others quotes accurate and well informed.

        (eg. Dan Walker referring yesterday to a Minister who “couldn’t tell me” the details of the vaccine transport contingency measures in place to cope with a no deal Brexit. Well, that was FAKE too. I watched the interview, and the Minister stated he WOULDN’T tell him the details, and also explained why.)

        And, it is nothing to do with opinions, either. I respect you have different opinions to me, but I try and show the other side of the coin by referring to accurate information on the other side of the coin. I do NOT supply false information to do that. I do NOT need to change reality to try and make a point.

        If you want to post in that way, and refer to the “we”, it is your choice. Not sure the “we” would find it that supportive, apart from the minority who do the same.

        (And, yes, there is a minority who support and a large number undecided. Which is what I have stated repeatedly. If you want to see those undecided become decided, I would suggest get to the point where gas is produced in commercial and economical volumes and you would see them decide, because they have NOT decided to join the antis in any great numbers over many quarters. Now, I have also posted that point will probably not be reached now, so we will probably not see that happen, but it DOES happen with most new concepts/products. Which is generally why such surveys are conducted over time in other situations, and those of us who have commissioned such, recognise that.)

        • Martin you are wrong and many can see you are wrong. I am not prepared to communicate with you further. Because it is you that over simplify and it is you that has distorted percentages and statistics in the past, not I. You ignore I mentioned fluctuation and trend as well as local opposition, MPs etc and other surveys. The governments wave survey is only one survey, there are other sources. And you persist in making your comments personal. You have falsely accused me of many things, including being indifferent to those suffering fuel poverty. All baseless. And most perceive the use of capitals unecessary and some perceive as aggressive. The bottom line is you are fighting a lost cause, there is a moratorium in place, the geology continues to look damning and all government policy is moving away from fracking and fossil fuels. Quite frankly, I will not waste further time on your bigotry.
          Merry Christmas

          • No, I am not fighting a lost cause, as my last statement made perfectly clear. (If the cause is lost, then why the anti need now to try and change the history?) Maybe a lost cause in expecting other posts being factually correct, but I, and others, can correct that and “many” (lol) can see “we” are correct. You have no need to waste time, and I do not see my time wasted correcting the record. That is a perfectly normal and expected use of a comment section within a publicly accessible Internet site. It just surprises me how normalized it is now for incorrect statements to be made on such platforms then shock and outrage when they are corrected. Why expect different reaction on the Internet to what happens in a pub?

            Sorry, but you can wriggle away into other areas, where you are still incorrect, but the point you made initially was, and remains, incorrect.

            The incorrect statement is what I corrected. I also use capitals to focus attention upon the point under discussion, as some have shown difficulty concentrating upon that, and are easily deflected. But, I do refrain from the use of Emojis and try and resist the use of the “we”, as both as commonly used instead of personal awareness and conviction.

            You like to call me aggressive-I am not, a bigot-I am not. Distorted percentages and statistics-I have not. You-accurate? Not always.

            However, do have an enjoyable, and safe Christmas, and I trust Santa’s navigation is accurate.

  5. Given our complex geology it seems the search for an indigenous supply of fracked gas is hors de-combat, a conclusion many of us welcome. As Kat says, we need less not more gas. Our government however has left the door open, seeing fracked gas as essential (ie cheaper) in the production of the hydrogen energy deemed essential in achieving net zero. Perhaps this is the point at which those who abhor the continuing development of fossil fuel technology should be concentrating their efforts – the electrolysis alternative to gas as a means of producing hydrogen.. Gas will in any case require CCS for treatment of emissions if we are to avoid overloading our atmosphere further, let alone achieving drawdown which is unlikely to benefit from these forms of CCS. A question at this point for the geologists: does our complex geology not render the underground storage of produced carbon extremely risky? Should we not be pursuing soil regeneration and drawdown more energetically, together with a full ban on fossil fuel development, as the simplest and most natural means of CCS and of combating climate change?

  6. Iaith 1720

    I do not see in any of the recent reports here on DOD that your assertion below is true on the 2 counts it mentions.

    Our government however has left the door open, seeing fracked gas as essential (ie cheaper) in the production of the hydrogen energy deemed essential in achieving net zero.


  7. Cripes – moved to the computer –

    1. That the government sees fracked gas as essential in the production of hydrogen.
    2. That hydrogen energy is essential in achieving net zero

    In the first case – as there is a moratorium now supported by the OGA report, HPHV fracking for gas is not going to happen.
    In the second case, hydrogen may well have a part in achieving net Zero, but only as part of a multi faceted program.

    On another issue you raise

    A question at this point for the geologists: does our complex geology not render the underground storage of produced carbon extremely risky?

    Reservoir engineers have been working for years on the thorny issue of CO2 storage in depleted reservoirs offshore. The N.Sea is blessed with many a depleted gas reservoir, especially in the Southern North Sea. The Humber gateway is a good example of offshore (non fracked gas) being used to produce hydrogen, and depleted reservoirs being used to store the CO2.

    At this level I do not see that at this point, the storage of CO2 in depleted reservoirs is extremely risky outwith the engineering challenges in putting it there. ie the storage of a gas in an offshore reservoir that held gas.

    I see that Equinor are looking at a green hydrogen project which seems to intimate the storage of hydrogen in depleted reservoirs (as gas storage), though if I look hard enough, perhaps someone intends to store CO2 in there as well.

  8. Thanks for your comments, Hewes62. Are you perhaps a geologist?
    I think you are nit-picking a little concerning my other points. It is true that the gas used, and I understand that 90% or so of hydrogen is produced by this method, may not be fracked gas, but my guess is that it will be. I should have been clearer. This 90% figure might no longer be valid: it’s sometimes difficult to date government publications.
    I took a similar short cut in stating that the government sees hydrogen energy as essential in achieving net zero. This is surely implied in the following two of the various statements to this effect in the recent White Paper.
    “We will generate new clean power….by investing in new hydrogen technologies.” (p 11 White Paper)
    “Given the pivotal role of electricity in delivering net zero emissions,…. (Costs) will depend on ….the cost and availability of other low-carbon technologies, particularly low-cost clean hydrogen.” (ibid. p 42)
    You also argue : “as there is a moratorium……….fracking for gas is not going to happen.” A moratorium is not a ban, (would that it were), and only by 2050 could electricity displace “to some degree, gas for heat in homes.” (ibid. p66). I hope you are right concerning the likelihood or otherwise of fracking in the UK, but it matters little where the gas is fracked. The following quotations are perhaps also relevant: “We will need investment in the gas network to support the ambition….for a potential Hydrogen Town before the end of the decade.” (ibid. p84) Moreover as recently as 2020 iGas were seeking authority to keep their Misson site and relevant permissions open in the event fracking was permitted again in the UK. It seems that not all are convinced of the good faith of this government.
    You may be right about the storage of CO2 in depleted reservoirs. My question was an open one and I sought reassurance from a geologist that what you say is true, and that our complex geology is not a safety issue here.

    • Iaith1720

      Not a geologist but a mining engineer with coal industry and oil industry experience. Hence interest in mining induced seismic events (probably caused a few) and subsidence (caused a lot), plus fracking in old coalfields where you have a much better knowledge of the geology – primarily because the old miners ran into all the faults first – (looks like we will not know in the UK now). Then carbon capture as it was looked at many years ago by oil companies in the UK et al.

      Re nit picking – yes it may seem so, but as we all seem to be on the same page re the larger issue (HVHP fracking for gas in the UK is not likely to happen) then we are left to pick out bits of what we say.

      Re gas used for conversion to Hydrogen. For the UK it will not happen as we will not do HPHV fracking for gas. Globally, I doubt it as well, but we shall see. Will we import large amounts of fracked gas to convert to hydrogen? Not sure, but we are more likely to happily keep importing Norwegian gas or (depending on the pipeline) Russian gas (and any LNG as there may well be plenty to go round). Time will tell.

      Re complex geology. Complex is a relative term. For a worked out coalfield, the geology may be complex, but well understood. Likewise, for a depleted reservoir, the geology may be complex (or simple once you understand it as I was often told), but its likely to be well understood. Hence the risks from storing gas in a depleted reservoir will be less than popping it into a bit of ground not well surveyed. Best put it somewhere you have had a good look at first (and its offshore so no aquifers to worry about or seismic event affects on onshore property?).

      Re the moratorium. Unless some fracking revolution turns up (and we have a long read here saying its not likely), I do not see the moratorium being lifted. Not sure why Missoni have kept their well, but one well in NE Notts will not lead to a fracking revolution I suspect.

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