The inherent complexity of the U.K.’s sedimentary basins has not been fully appreciated or articulated and, as a result, its suitability for hydraulic fracturing has been overhyped, according to expert analysis from Edinburgh, U.K.-based Heriot-Watt University.
Horizontal multistage fracturing has led to a resurgence in oil and gas production across North America over the past decade, upending global energy markets and creating an oversupply that has led to a three-year slump in prices.
Professor John Underhill, Heriot-Watt University’s chief scientist, challenged the implication that because fracking works in the U.S. it must also work in the U.K.
“Both sides of the hydraulic fracturing debate assume that the geology is a ‘slam dunk’ and it will work if exploration drilling goes ahead,” Underhill said in a statement. “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 U.K. The inherent complexity of the sedimentary basins has not been fully appreciated or articulated and, as a result, the opportunity has been overhyped.”
The theory may soon be challenged as U.K.-based Cuadrilla begins drilling a pilot well in the north of England as a first step toward testing the commerciality of shale gas production in the U.K. It has permission to drill four horizontal wells that it intends to hydraulically fracture, a process that has become highly controversial in many European counties and banned in some. Cuadrilla hopes to analyze results from the pilot well this year, as well as drill the horizontal wells and possibly begin the fracking process.
55 million years too late
A significant tilt affects the U.K., 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, according to the Heriot-Watt analysis.
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.
“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 U.K.'s gas needs only to discover that we’re 55 million years too late,” Underhill said.
Writing in The Conversation , he 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 65 and 145 million 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 290 million years ago. This has further compounded their structural complexity.