UK shale gas: fracking potential dramatically revised downwards

In 2013, much to the joy of the British government and the fracking industry, the British Geological Survey (BGS) declared that there was likely to be between 24 and 68 trillion m3 (TCM) of gas available to fracking ventures in the Carboniferous Bowland Shale, the most promising target in Britain. That is equivalent to up to about 90 years’ supply at the current UK demand for natural gas.  The BGS estimate was based on its huge archives of subsurface geology, including that of the Bowland Shale; they know where the rock is present and how much there is. But their calculations of potential gas reserves used data on the gas content of shales in the US where fracking has been booming for quite a while. Fracking depends on creating myriad cracks in a shale so that gas can escape what is an otherwise impermeable material.

Bowland Shale 1
Areas in Britain underlain by the Bowland Shale formation (credit: British Geological Survey)

How much gas might be available from a shale depends on its content of solid hydrocarbons (kerogen) and whether it has thermally matured and produced gas that remains locked within the rock. So a shale may be very rich in kerogen, but if it has not been heated to ‘maturity’ during burial it may contain no gas at all, and is therefore worthless for fracking. Likewise, a shale from which the gas has leaked away over millions of years. A reliable means of checking has only recently emerged. High-pressure water pyrolysis (HPWP) mimics the way in which oil and gas are generated during deep burial and then expelled as once deep rock is slowly uplifted (Whitelaw, P. et al. 2019. Shale gas reserve evaluation by laboratory pyrolysis and gas holding capacity consistent with field data. Nature Communications, v. 10, article 3659; DOI: 10.1038/s41467-019-11653-4). The authors from the University of Nottingham, BGS and a geochemical consulting company show that two samples of the Bowland Shale are much less promising than originally thought. Based on the HPWP results, it seems that the Bowland Shale as a whole may have gas reserves of only around 0.6 TCM of gas that may be recoverable from the estimated 4 TCM of gas that may reside in the shale formation as a whole. This is ‘considerably below 10 years supply at the current [UK] consumption’.

Unsurprisingly, the most prominent of the fracking companies, Cuadrilla, have dismissed the findings brusquely, despite having published analyses of other samples that consistent with results in this paper. Opinion in broader petroleum circles is that the only way of truly putting a number to potential reserves is to drill and frack many wells … The British government may well have a collective red face only a week after indicating that they were prepared to review regulation of fracking, which currently forces operations to stop if it causes seismic events above magnitude 0.5 on the Richter scale. A spokesperson for Greenpeace UK said that, ‘Fracking is our first post-truth industry, where there is no product, no profit and no prospect of either.’

See also: McGrath, M. 2019. Fracking: UK shale reserves may be smaller than previously estimated. (BBC News 20 August); Ambrose, J. 2019. Government’s shift to relax shale gas fracking safeguards condemned (Guardian 15 August); Fracking in the UK; will it happen? (Earth-logs June 2014)

Fracking in the UK; will it happen?

Whether or not one has read the Tractatus Logico-Philosophicus of Ludwig Wittgenstein, there can be little doubt that one of his most famous quotations can be applied to much of the furore over hydraulic fracturing (fracking) of hydrocarbon-rich shale in south-eastern Britain: ‘Whereof one cannot speak, one must remain silent’ (more pithily expressed by Mark Twain as ‘Better to remain silent and be thought a fool than to speak and remove all doubt’). A press release by the British Geological Survey  in late May 2014 caused egg to appear on the shirts of both erstwhile ‘frackmeister’ David Cameron (British Prime Minister) and anti-fracking protestors in Sussex. While there are oil shales beneath the Weald, these Jurassic rocks have never reached temperatures sufficient to generate any significant gas reserves (see: Upfront, New Scientist, 31 May 2014 issue, p. 6). Yet BGS estimate the oil shales to contain a total of 4.4 billion barrels of oil. That might sound a lot, but the experience of shale fracking companies in the US is that, at best, only about 5% can be recovered and, in cases that are geologically similar to the Weald, as little as 1% might be expected. Between 44 and 220 million barrels is between two and six months’ worth of British oil consumption; and that is only if the entire Wealden shales are fracked.

Areas where petroleum-rich shales occur at the surface in Britain. (credit: British Geological Survey)
Areas where petroleum-rich shales occur at the surface in Britain. (credit: British Geological Survey)

Why would any commercial exploration company, such as Cuadrilla, go to the trouble of drilling wells, even of an ‘exploratory nature’, for such meager potential returns? Well, when there is sufficient hype, and the British Government has gushed in this context for a few years, bigger fish tend to bite and cash flows improve. For instance, Centrica the owner of British Gas forked out $160 million to Cuadrilla in June 2013 for a quarter share in the well-publicised licence area near Blackpool in Lancashire; the grub stake to allow Cuadrilla to continue exploration in exchange for 25% of any profit should commercial quantities of shale-gas be produced.

Sedimentary rock sequences further north in Britain whose geological evolution buried oil shales more deeply are potential gas producers through fracking; an example is the Carboniferous Bowland Shale beneath the Elswick gasfield in west Lancashire, targeted by Cuadrilla. Far greater potential may be present in a large tract of the Pennine hills and lowlands that flank them where the Bowland Shale occurs at depth.

Few people realize just how much detail is known about what lies beneath their homes apart from maps of surface geology. That is partly thanks to BGS being the world’s oldest geological survey (founded in 1835) and partly the sheer number of non-survey geologists who have prowled over Britain for 200 years or more and published their findings. Legally, any excavation, be it an underground mine, a borehole or even the footings for a building, must be reported to BGS along with whatever geological information came to light as a result. The sheer rarity of outcropping rock in Britain is obvious to everyone: a legacy of repeated glaciation that left a veneer of jumbled debris over much of the land below 500m that lies north of the northern outskirts of the London megalopolis. Only highland areas where glacial erosion shifted mullock to lower terrains have more than about 5% of the surface occupied by bare rock. Of all the data lodged with BGS by far the most important for rock type and structure at depth are surveys that used seismic waves generated by vibrating plates deployed on specialized trucks. These and the cables that connected hundreds of detectors were seen along major and minor roads in many parts of Britain during the 1980s during several rounds of licenced onshore exploration for conventional petroleum resources. That the strange vehicles carried signs saying Highway Maintenance lulled most people apart from professional geologists as regards their actual purpose. Over 75 thousand kilometers of seismic sections that penetrated thousands of metres into the Earth now reside in the UK Onshore Geophysical Library (an Interactive Map at UKOGL allows you to see details of these surveys, current areas licenced for exploration and the locations of various petroleum wells).

Seismic survey lines in northern England (green lines) from the interactive map at the UK Onshore Geophysical Library
Seismic survey lines in northern England (green lines) from the interactive map at the UK Onshore Geophysical Library

Such is the detail of geological knowledge that estimates of any oil and gas, conventional or otherwise, residing beneath many areas of Britain are a lot more reliable than in other parts of the world which do not already have or once had a vibrant petroleum industry. So you can take it that when the BGS says there is such and such a potential for oil or gas beneath this or that stretch of rural Britain they are pretty close to the truth. Yet it is their raw estimates that are most often publicized; that is, the total possible volumes. Any caveats are often ignored in the publicity and hype that follows such an announcement. BGS recently announced that as much as 38 trillion cubic metres of gas may reside in British shales, much in the north of England. There followed a frenzy of optimism from Government sources that this 40 years’ worth of shale gas would remove at a stroke Britain’s exposure to the world market of natural gas, currently dominated by Russia, and herald a rosy economic future to follow the present austerity similar to the successes of shale-gas in North America. Equally, there has been fear of all kinds of catastrophe from fracking on our ‘tight little island’ especially amongst those lucky enough not to live in urban wastelands. What was ignored by both tendencies was reality. In the US, fracking experience shows that only 10% at most of the gas in a fractured shale can be got out; even the mighty Marcellus Shale of the NE US underlying an area as big as Britain can only supply 6 years of total US gas demand. Britain’s entire shale-gas endowment would serve only 4 years of British gas demand.

To tap just the gas in the upper part of the Bowland basin would require 33 thousand fracking wells in northern Britain. Between 1902 and 2013 only 19 onshore petroleum wells were drilled here in an average year. To make any significant contribution to British energy markets would require 100 per annum at a minimum. Yet, in the US, the flow rate from fracked wells drops to a mere zephyr within 3 years. Fracking on a large scale may well never happen in Britain, such are the largely unstated caveats. But the current hype is fruitful for speculation that it will, and that can make a lot of cash sucked in by the prospect – without any production whatsoever.

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