Calls for 600m shale gas fracking limit
Prof Richard Davies (credit Durham University)
Shale gas "fracking" should only take place at least 600 metres down from aquifers used for water supplies, researchers have said.
A new study by Durham University scientists revealed the process, which uses high-pressure liquid pumped deep underground to split shale rock and release gas, caused fractures running upwards and downwards through the ground of up to 588 metres from their source.
The research, published in the journal Marine and Petroleum Geology, found the chance of a fracture extending more than 600 metres upwards was exceptionally low, and the probability of fractures of more than 350 metres was 1 per cent.
Researchers said the study showed it was "incredibly unlikely" that fracking at depths of 2km to 3km below the surface would lead to the contamination of shallow aquifers which lie above the gas resources.
Shale gas extraction has been controversial in the US because of claims that cancer-causing compounds used in the process have polluted water supplies and that the flammable methane gas itself can pollute drinking water.
But Professor Richard Davies, of Durham University, said it was more likely any contamination came from drilling down through rock containing methane and where the cement or steel well casing may fail, rather than the separate fracking procedure carried out several kilometres down where shale gas forms.
In most cases fracking occurs around 2km to 3km below the surface, where geological conditions are right for shale gas to form, but in one case in Wyoming it took place at around 600 metres down and there was now evidence of chemicals in the water supply.
Prof Davies said there was "just reason to be cautious" and said regulators should set a distance limit, which should be well in excess of 600 metres when fracking in new areas where there was no existing data on possible fractures.
He said the UK's only shale gas exploration scheme near Blackpool, carrying out fracking 3km down, would not affect water supplies in the area, which are around 300 metres below the surface.
The scheme was halted last year after it caused two small earthquakes but could get the go-ahead to resume, while other areas are being considered for exploration.
The researchers from Durham University, Cardiff University and the University of Tromso, Norway, looked at thousands of natural and induced rock fractures in the US, Europe and Africa and found none of the artificially caused ones were more than 600 metres.
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