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'Highly probable' fracking caused quakes, says report

It is “highly probable” that the controversial process of hydraulic fracturing to create shale gas off the coast of Blackpool triggered two earthquakes earlier this year, a report revealed today.

Two seismic events — one of magnitude 2.3 in April and another of 1.5 in May — were the focus of the report but another 48 weaker seismic events were also detected by the British Geological Survey following activities by developer Cuadrilla to extract shale gas. These water injection operations were taking place over 3km below the earth’s surface and around 3.5km east of the outer limits of Blackpool.

Cuadrilla suspended its drilling operations — known as fracking — at Preese Hall-1 well near Blackpool in early June ahead of commissioning the report.

An “unusual combination of factors” caused the seismic events (see below), including the geology of the well site coupled with the pressure exerted by water injection, it was reported. The report concluded that this combination of factors was “unlikely to occur” again at future well sites but that if it did then local geology would mean seismic events of around magnitude 3 could occur as a worst case scenario.

The report recommended that Cuadrilla install an early detection system to mitigate the escalation of seismic events and in turn, the chance of any future seismic event exceeding safe limits — it said that based on internationally accepted German standards a maximum seismic magnitude of 2.6 should be used.

“We are ready to put in place the early detection system that has been proposed in the report so that we can provide additional confidence and security to the local community,” said Cuadrilla Resources chief executive Mark Miller. “Cuadrilla is working with the relevant local and national authorities to implement the report’s recommendations so we may safely resume our operations.”

The report has been submitted to the Department of Energy and Climate Change (Decc) and the British Geological Survey, the latter acting in its capacity as adviser to Decc.

An ‘unusual combination of factors’

The report indicates that a number of factors coincided to cause the seismic events:

  1. The Preese Hall-1 well encountered a pre-existing critically stressed fault
  2. The fault was transmissible so it accepted large quantities of fluid
  3. The fault was brittle enough to fail seismically
  4. The repeated seismicity was most likely induced by repeated direct injection of fluid into the same fault zone
  5. The strongest events took place around 10 hours after the injection because the pressure spread out over a larger area
  6. It is unlikely that the actual opening of the hydraulic fractures induced the seismic events because there is a delay of many hours between the injection of fluid and the strongest seismic event. Fluid pressure on the fault, however, has a natural time scale which fits with the observed delay
  7. The chance of any one of these factors occurring is small, therefore the probability of a repeat occurrence of a fracture-induced seismic event with similar magnitude in the Bowland basin is very low

Readers' comments (5)

  • I am a graduate geotechnical engineer working in the southwest of England. I am just reading from a number of sources about the outcome of the report investigating the Blackpool Earthquakes. I am horrified as a young engineer to see that something that has caused seismic events, and has the potential to do a number of damages to health and the environment, was granted permission in the first place, let alone be allowed to continue. As a group of responsible individuals, shouldn't civil engineers be speaking up about such unethical and hazardous operations?

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  • If I read point 7 correctly then it was just by chance a very vulnerable site was elected for the trial drilling. Surely more extensive trials are needed to prove statistically that their actually is minimal risk of the recurrence of such chance circumstances at other sites.

    Point 4 - If it is known the seismic event occurred because of the injection into a fault zone why go ahead and repeat the process causing a second seismic event.

    To my mind the report raises as many questions as it answers.

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  • From the Report extracts given here it seems that these operations can re-start. However, we must await the experts’ responses to queries raised by reviewers.
    Given the proposed instrumentation monitoring there should be no problems. "The fault was brittle enough to fail seismically"; "It is unlikely that the actual opening of the hydraulic fractures induced the seismic events"; "the probability of a repeat occurrence of a fracture-induced seismic event with similar magnitude in the Bowland basin is very low".
    It appears that fracking, itself, did not cause these seismic events at a brittle seismic sensitive fault which would normally, and could, be induced at this site at any time by other “natural” events.
    These 2 micro seismic events should also be judged alongside the extensive records of frequent similar seismic events in this area over many years, and often at strengths far higher, even the low probability Richter 3 limit suggested. Effectively, available evidence suggests that little or no damage or injuries have previously occurred even with higher strength “shocks” and should not occur any differently due to fracking operations.
    Peter Wilson (M)

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  • As a civil engineer of over 35 years' experience, including a number of years in the Oil & Gas field, I am concerned at the comments from Messrs Adcock and Thomas, whom I presume to be members of our profession. Their comments reflect the popular preoccupation with emotive language in preference to reasoned scientific analysis that has blighted the development of our infrastructure over the past number of decades. It has become fashionable to doubt or simply dismiss the findings and opinions of expert engineers and scientists as a matter of course and this has systematically undermined society's ability to plan and implement infrastructural development in an orderly manner. As engineering professionals we should be able to rise above this and form our opinions based on (a) the known scientific facts and (b) the informed professional opinions of experts who are better qualified than we to form such opinions. As Peter Wilson has said, we should await the experts' responses to valid queries raised before forming a final view on this issue. However, to dismiss the findings of this report out of hand is to lower ourselves to the level of the popular media and does a disservice to our profession.

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  • I am suprised at the shock expressed above, it has long been known that underground mining methods can alter the equilibrium of forces within the ground. Considerable research has been undertakeninto mining induced landslides, earthquakes and fault reactivation. Although fracking is a relativley new extraction technology the potential for these effects in the right geological circumstance has always been obvious. Society needs minerals, including oil and gas, to survive. Careful study into the consequences of all mineral extraction is required by european directive and any Environmental Impact Assessment worth its salt would consider the likelihood and magnitude of these events and ways for society to manage and mitigate their impact.

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