Research

Surrey earthquakes unlikely to be caused by oil activity, say researchers

190504 BGS chart newdigate

A new study has found no clear links between the recent swarm of earth tremors in Surrey and local oil drilling activity.

According to the paper, there have been 129 seismic events centred  between the villages of Newdigate and Charlwood since 1 April 2018.

But based on the available evidence, the authors concluded it was unlikely that nearby industrial activities had induced the swarm.

The study, submitted to the journal, Seismological Research Letters, uses recorded seismic data and operational information provided by operators at oil exploration sites at Horse Hill, near Gatwick Airport, and Brockham, near Dorking.

Most of these tremors were recorded on a network of temporary seismometer stations installed in the area in July and August 2018 after the first nine seismic events.

The largest tremor in the swarm had a magnitude of 3.1ML. 31 events exceeded 0.5ML but only 11 were felt, based on reports recorded by the British Geological Survey (BGS). The most recent tremor reported by the BGS was on 17 May 2019.

1810 Horse Hill UKOG2

Horse Hill oil site near Gatwick Airport, October 2018. Photo: Used with the owner’s consent

UK Oil & Gas, the main investor in the Horse Hill site, and Angus Energy, the operator at Brockham, have repeatedly said their activities did not cause the tremors.

The paper, which has not yet been peer-reviewed, has been posted online and lead author, seismologist, Dr Stephen Hicks, of Imperial College, welcomes scientific feedback. The final published version may change.

“Background seismicity”

The authors said the average depth of the tremors was 2.3km, below the target formations at Horse Hill. The well, Horse Hill-1 (HH-1) is exploring the Portland sandstone at a depth of 600m and the Kimmeridge shale at 800m, they said.

If the tremors had been induced it was a novel mechanism that has not been documented in scientific literature, Dr Hicks told BBC Radio.

He said the tremors, based on data available at present, were likely to be part of the background seismicity of the UK. Ancient faults could be stressed by tectonic forces in the Alps and Mediterranean, he said. This could cause seismic slip to be released along faults running east-west in the Weald.

The study’s conclusions were based on six key points:

  1. Timing
    The authors said the sequence of seismic events started before subsurface activity and flow testing/production began at HH-1 in 2018
  2. Location
    The earth tremors were 3km from the nearest oilfield operations at HH-1 and deeper than the target formations. This would be an unusual location for induced seismicity caused by the current scale of operations, the authors said. They found no clusters of seismicity immediately close to the drill site.
  3. Oil activities
    Based on operational logs provided by the operators, the authors said they found no clear link between the seismicity rate and cumulative oil production or activities at either HH-1 or Brockham. Some events happened when the HH-1 well was shut-in, they said. But if this were a factor, any correlation was not yet robust and such a stress transfer mechanism was unclear, Dr Hicks said.
  4. Mechanism
    The authors did not find any abnormal faulting mechanisms that had been previously observed for production-induced seismicity, such as at Groningen in the Netherlands. The observations were consistent with reactivation of a pre-existing fault, they said.
  5. Volume and stress
    The cumulative volumes of net production reported by the operators were much smaller than past reported cases of extraction-induced seismicity, the authors said.
  6. Fluid pathways
    There were no obvious connections between Horse Hill and Newdigate Faults, which could plausibly offer a permeability pathway from HH-1 to the earthquakes, the paper concluded. The borehole does not directly intersect the Horse Hill fault, it said.

The study recommended seismic monitoring should be carried out close to hydrocarbon development and production sites. Operational activities, such as well shut-in periods, and production volumes and rates should be reported to reduce uncertainties for similar cases in future, it added.

Seismological Research Letters

58 replies »

  1. So how about identifying the probable causes and carrying out scientific seismic monitoring in the vicinity of the most likely culprits?

    Something must have caused the swarm of earthquakes in this previously earthquake free zone!

    • Peter – it seems like you missed the classes at school where they taught you that earthquakes happen naturally

      • Judith, that’s exactly why I made my suggestion!
        Earthquakes have been occurring for millennia long before humans starting interfering with deep drilling and powerful explosions.
        So if nature caused this unprecedented swarm of earthquakes in this location why didn’t the ‘experts’ simply say so?
        Cuadrilla denied a connection between their fracking operations and the swarm of earthquakes around Weeton village for months before they accepted the blindingly obvious. At least there were no denials from them this time about the link between their fracking operations at Preston New Road and the 50 plus nearby earthquakes last Autumn.
        Although they did attempt to minimise the potential consequences at depth through the farcical ‘melongate’ propaganda.

        • Peter – experts have all said the Surrey earthquakes were natural. The reason why Cuadrilla initially didn’t “admit” the tremors at Preese Hall were due to fracking is that the events were detected using geophones that were situated a great distance away. The initial event locations indicated that the hypocentre of the events was away from the area being fracked. It wasn’t until the velocity model was refined and the events relocated that it became clear that fracking caused the seismicity

  2. How about it, Peter?

    Ermm-done, and continuing. I think you will find the experts have suggested this is just a natural occurrence that happens hundreds of times a year in the UK, often in places where seismic events have not occurred previously for many years.

  3. I wonder why UKOG gave site information to Dr Hicks but wont release any to those who say there may be a link ? Oh , I know .

  4. Well there we go. Hopefully the antis will shut up about earthquakes now. Wonder what they will latch onto next?

    • John- I wouldn’t hold you’re breath. The antis don’t do science and they’ll find some way of arguing that Dr Hick’s paper is a big conspiracy funded by the oil industry.

      • Judith – I’m happy to accept a well-researched report.
        John – earthquakes are an issue. If some are not caused by drilling that’s fine, but if some ARE caused by drilling then that’s not acceptable. So we will not shut up about earthquakes. 🙂

        • David – are you also going to object to all other industrial processes that cause tremors? If so you can say goodbye to geothermal energy, hydroelectric energy and any renewable energy that relies on elements that are mined from the subsurface

  5. Sadly Judith, I think you’re right. They really are a bunch of fanatics. I can’t understand them at all.

  6. It really doesn’t matter which side of the fence you sit on, surely no one can think, in view of the scientific evidence to the contrary ,that ANY exploration and production of fossil fuels is a good thing??

    • It’s good if you want to live in a modern society and have things like clothes, medicine and warm homes.

    • Well it keeps you communicating Dianna! Whether anyone thinks that is a good thing I don’t know, but you seem to enjoy that opportunity. I suspect those in disaster zones (eg. serious earthquakes) where many more are rescued and assisted now because of fossil fuel think it quite good also. Press your plastic button on your TV next time one is being reported on the news, and see the helicopters, diggers, generators, chain saws etc. being mobilised. Looks very much like a good thing to me.

  7. Dianna, I assume from your statement that you hold by your statement & have completely “de-fossilised” yourself from using any fossil fuels, directly or indirectly?

  8. Interesting to read the condescending put downs, I assume they have science and facts to support such statements as “the antis don’t do science” etc? Because surely such intelligent, scientific people such as they don’t resort to smear, stereotyping and generalisations? I presume Professors of Petroleum Geology that have concerns about fracking may have some scientific knowledge? And interesting to recall how some of those making comments today on this forum that support fracking make excuses when the science and data doesn’t go their way or support their arguments. Does that mean they don’t do science either? 😉

    • “Humanity really does need to pay attention to arithmetic and the laws of physics.”

      Professor Sir David McKay-late government chief scientific adviser.

      Good enough, KatT? Not too much of a smear, just reality.

      He also stated:

      “There is this appalling delusion that people have that we can take this thing (renewables) and we can just scale it up, then we can just do energy efficiency.” Hmm, now that seems very familiar.

  9. Its surely the late easter bunny hopping through the fields! Thats fair hopping to cause such a magnitude of tremors!

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