Heriot Watt University geologist warns that folding and fracturing of rocks may have had a detrimental effect on evolution and recoverability of UK shale gas
The potential for recovering shale gas by fracking in the UK may have been overhyped, because the geological history of the region has been overlooked, Prof John Underhill, chief scientist at Heriot Watt’s Institute of Petroleum Engineering has warned.
Plate tectonics and the effects of volcanism millions of years ago may have deformed the rocks in which hydrocarbon deposits form, prevent their formation in the first place or making them uneconomical to recover. This would mean that the debate over the environmental effects of fracking is a sideshow, said Underhill: “Both sides of the hydraulic fracturing debate assume that the geology is a ‘slam dunk’ and it will work if exploration drilling goes ahead. The inherent complexity of the sedimentary basins has not been fully appreciated or articulated and, as a result, the opportunity has been overhyped.
In the US and Eastern Europe, where shale gas is plentiful, deposits formed in the middle of continental plates. But this is not true of the UK, which is at the edge of a continental plate and its geology is, therefore, vulnerable to deformation by the effects of plate tectonics. The crucial event in this case, according to Prof Underhill, was the formation of the Atlantic Ocean 55 million years ago, accompanied by an upward surge of molten magma under Iceland. This surge tilted the rocks that now make up the UK and pushed the sedimentary basins where material had collected that would be turned into natural gas by the heat and pressure of overlying rocks against the stable geology of continental Europe.
This would have two effects, Prof Underhill said. First, the sedimentary material would have been lifted up to a level where they would no longer generate petroleum. Second, the geological processes pressing the basins against the continental geology would have folded and fractured the shales where deposits may have already formed into compartments and faults along which gas may have escaped.
“There is a need to factor this considerable and fundamental geological uncertainty into the economic equation,” he said. “It would be extremely unwise to rely on shale gas to ride to the rescue of the UK’s gas needs only to discover that we’re 55 million years too late.”
Three potential fracking sites, the Weald Basin in south-east England, the Bowland Shale in Lancashire and the West Lothian Oil Shale in Scotland are all known to have undergone geological deformation since their formation, Prof Underhill noted, leading to complex structures in their rocks and uncertainty as to whether they would yield economic amounts of gas.
The technical director of fracking firm Caudrilla, Mark Lappin, told the BBC that the company wants to undertake drilling tests to better understand the nature of shale deposits under the UK. The British Geological Survey (BGS) estimated that there were large potential gas reserves but has not done research that would confirm Prof Underhill’s suspicions. “It’s the purpose of our current drilling operations to better understand the reserve, reduce speculation from all sides and decide if and how to develop it,” Lappin told the BBC News website. “I expect Professor Underhill would be supportive of the effort to understand the resource including geological variation.”