Fracking near geological faults in former coal mining areas could trigger earthquakes and should not take place without careful assessment of all available geological data, according to one of the UK’s leading experts on the subject.
Professor Peter Styles, a former adviser to David Cameron, said the fracking process could lead to seismic activity by stimulating faults in geology that was already stressed by mining.
The retired academic, who linked Cuadrilla’s fracking in Lancashire with the 2011 Blackpool earthquakes, believes this could jeopardise the shale gas industry.
He said fracking should not be carried out within 850m of a fault in any area. But in mining regions he suggested the risk could be greater:
“We have already changed the stress in these areas by removing the coal and allowing the ground above to subside.
“We have already preconditioned the faults. Even when mining stops it is still possible to have seismicity, as we have seen recently around Ollerton and Thoresby in Nottinghamshire.”
He told DrillOrDrop there could be hundreds of faults near shale gas sites that companies may not know about.
He said some faults were too small to be identified on geological maps or seismic surveys but were still big enough to cause the 0.5 magnitude earthquakes that under UK regulations would stop fracking.
His comments would appear to raise questions about fracking in large parts of the Bowland Shale, which lies under the Coal Measures from the East Midlands and Yorkshire to parts of Lancashire and Cheshire. They could also have implications for the seismic surveys being carried out across shale gas areas.
Professor Styles is a former President of the Geological Society of London, a project leader with the ReFine fracking research project and previous Head of Geology at Keele University.
He said he had identified faults close to proposed shale gas sites using detailed underground mining records. He called for these records to be taken into account when decisions were made about fracking sites.
Traffic light warning
The UK’s regulation on induced earthquakes – known as the traffic light system – requires shale gas companies to stop fracking if they detect seismic activity at a magnitude of 0.5.
Professor Styles said:
“There are 10s, perhaps 100s, of small faults, measuring 25-50m long, to which a 0.5M earthquake corresponds. They have not been mapped on the surface or by the British Geological Survey.
“There are faults present near some of the proposed boreholes – 10s of metres away.
“There are faults that have experienced seismicity which are much closer to the boreholes than the companies possibly understand.
“I already have evidence that these faults have caused seismic activity.”
Asked by DrillOrDrop if he thought fracking in mining areas near pre-existing faults should be banned, he said “Yes”.
“If you wanted to establish a secure future for shale gas wells in the UK, I probably wouldn’t advise doing it in areas that have already been undermined.”
“If you could be 850m away from a fault, you would probably be ok. If you can’t be 850m away from that fault then there could be problems.”
Seismic surveys not fit for purpose?
Professor Styles suggested that the seismic surveys currently being carried out across Northern England would not identify small faults that could lead to a 0.5ML earthquake.
An earthquake of this size could be induced by a fault displaced vertically by as little as 1m, he said. But seismic surveys detected displacement – known as the throw – down to only 5m or 10m.
“Seismic surveys are adequate to define the big faults. Faults with throws of 100m are a problem. But faults that are much smaller than that are also a problem.”
Professor Styles said:
“The faults that are going to stop fracking are five times less than the resolution of the [seismic survey] tool we are looking for them with.
“That means that seismic reflections will give you the bigger faults but below that level there are faults that are capable of giving you earthquakes that would stop fracking.”
Inducing a ban?
Professor Styles said he feared the government would stop fracking in England if the industry activated a fault and induced an earthquake bigger than 0.5 magnitude.
This is much smaller than the fracking-induced earthquake in Blackpool in 2011, which measured 2.3ML.
Professor Styles said:
“If the industry carries on with this, there is a good chance they will affect one of these faults capable of inducing an earthquake of 0.5 ML. They would be forced to stop fracking.
“That is not a very sensible approach to moving this forward towards energy security.
“What I would hate is for this to go ahead and for it to go catastrophically wrong.
“These will not be big earthquakes, and may not be discernible by the population. But we have regulated to say that if a certain magnitude happens then fracking will stop.”
“I’m an advocate of us stabilising our energy supply sustainably and not offshoring our environmental responsibilities to Russia, Qatar and Algeria. But it has to be done right.
“I do not want this to go ahead willy-nilly without a proper appraisal of what might happen.
“In these mining areas, which cover a lot of the areas identified by BGS [British Geological Survey] as a prospective source for the Bowland Shale, there is a lot of information that should be taken into account before we charge too deeply into this.”
He said that it may also be difficult to distinguish between earthquakes induced by fracking and those by mining:
“Earthquakes happen after mining has stopped”.
He said he had advised the government that all available information should be considered as part of the planning process.
Coal Board engineers and surveyors had recorded faults as small as a few centimetres, he said. These records had been analysed by Liverpool University researchers and can now be used to overlay proposed and actual shale gas sites.
“We only know about these small faults because we have the mining records. Everywhere that was mined by the National Coal Board, there are maps of underground faults.
“There is information that the companies may be unaware of. I would hate to think that I failed to point out what I do know.”
Rejecting the idea of a blanket moratorium on fracking, he said:
“I am interested in us having information to hand and informed planning with the information that is available.
“We have forgotten about mining. Mining has not forgotten about us.”