The UK's geology unlikely to support fracking



Expert analysis from Heriot-Watt suggests that the UK's geology is unlikely to be suitable for hydraulic fracturing.

The inherent complexity of the sedimentary basins has not been fully appreciated or articulated and, as a result, the opportunity has been overhyped.

Professor John Underhill

While many opponents of fracking continue to focus on the environmental impact of this method of oil and gas extraction, Professor John Underhill, the University's Chief Scientist, has challenged the implication that because fracking works in the US it must also work in the UK.

Professor Underhill explains, “Both sides of the hydraulic fracturing debate assume that the geology is a ‘slam dunk' and it will work if exploration drilling goes ahead.

“In locations where the geology has led to large potential deposits, uplift and the faulted structure of the basins are detrimental to its ultimate recovery. Yet, the only question that has been addressed to date is how large the shale resource is in the UK. The inherent complexity of the sedimentary basins has not been fully appreciated or articulated and, as a result, the opportunity has been overhyped.”

A significant tilt affects the UK, which was initiated by active plate margin forces over 55 million years ago, due to an upward surge of magma under Iceland and the subsequent formation of the Atlantic Ocean. The latter led to buckling of precursor sedimentary basins against the stable tectonic interior of continental Europe, including those considered to contain large shale resources.

Areas that were once buried to depths and at temperatures where oil and gas maturation occurs, have been uplifted to levels where they are no longer actively generating petroleum. They have also been highly deformed by folds and faults that cause the shales to be offset and broken up into compartments. This has created pathways that have allowed some of the oil and gas to escape.

Professor Underhill said, “There is a need to factor this considerable and fundamental geological uncertainty into the economic equation. 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.”

Writing in The Conversation, John Underhill discusses three potential fracking sites to illustrate the issue: the Weald Basin in southern England, the Bowland Shale in Lancashire and the West Lothian Oil Shale in Scotland.

The Weald Basin of southern England was a major area of sedimentary deposits in the Cretaceous, (the period between 65m and 145m years ago) but was subsequently deformed into a major anticlinal arch - a type of fold that is an arch-like shape and has its oldest beds at its core.  The margins of this tectonic fold are particularly well defined since they are marked by the steeply dipping chalk ridges that form the North and South Downs in south-east England.

Other basins believed to contain commercial shale gas, like the Bowland Shale in Lancashire and West Lothian Oil Shale in Scotland, went through an additional period of deformation about 290m years ago. This has further compounded their structural complexity.