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Fracking check list

Bergung der Opfer des Grubenunglücks

Aftermath of the 1906 mine explosion at Courrières, northern France; the largest mining disaster in Europe with 1099 fatalities. Image via Wikipedia

Britain is on the cusp of a shale-gas boom (see Britain to be comprehensively fracked? : EPN 14 October 2011) and it is as well to be prepared for some potential consequences. In extensively fracked parts of the US – the states of New York, Pennsylvania, Texas and Colorado – there are reports of water taps emitting roaring flames after dissolved methane in groundwater ignites. This is largely due to common-place household water supplies from unprocessed groundwater, which are rare in Britain. But there are other hazards (Mooney, C. 2011. The truth about fracking. Scientific American, v. 305 (Nov 2011), p. 62-67) that have enraged Americans in affected areas, which are just as likely to occur in Britain. In fact the nature of shale-gas exploitation by horizontal drilling beneath large areas poses larger threats in densely populated area, as the people of Blackpool have witnessed in the form of small earthquakes that the local shale-gas entrepreneur Cuadrilla admit as side effects of their exploratory operations .

Chris Mooney succinctly explains the processes involved in fracking shale reservoirs; basically huge volumes of water laced with a cocktail of hazardous chemicals and sand being blasted into shales at high pressure to fracture the rock hydraulically and create pathways for natural gas to leak to the wells. One risk is that this water has to be recovered and stored in surface ponds for re-use. About 75% returns to the surface and also carries whatever has been dissolved from the shales, which can be extremely hazardous. By definition a shale containing hydrocarbons creates strongly reducing conditions, which in turn can induce several elements to enter solution as well as easily dissolved salts; for instance divalent iron (Fe2+) is highly soluble, whereas more oxidised Fe3+ is not, so waters having passed through gas-rich shales will be iron-rich. But that is by no means the worst possibility; one of the most common iron minerals in sedimentary rocks is goethite (FeOOH), which adsorbs many otherwise soluble elements and compounds. In reducing conditions goethite can break down to release its adsorbed elements, among which is commonly arsenic. The blazing faucet hazard results from hydrocarbon gases leaking through imperfectly sealed well casings to enter shallow groundwater, where the gases can also create reducing conditions and release toxic elements and compounds into otherwise pure groundwater by dissolution of ubiquitous goethite, as in the infamous arsenic crisis of Bangladesh and adjoining West Bengal in India where natural reducing conditions do the damage.

What is not mentioned in the Scientific American article is the common association of hydrogen sulfide gas with petroleum, produced from abundant sulfate ions in formation water by bacteria that reduce sulfate to sulfide in the metabolism. This ‘sour gas’, as it is known in the oil industry, is a stealthy killer: at high concentrations it loses its rotten-eggs smell and in the early days of the petroleum industry killed more oil workers than did any other occupational hazard. Visit the spa towns of Harrogate in Yorkshire and Strathpeffer in northern Scotland and sample their waters for examples of what Carboniferous and Devonian gas-rich shales produce quite naturally: noxious stuff of questionable efficacy. The environmental effects of such natural seepage from gas-rich rocks tell a cautionary tale as regards fracking. The highly reducing cocktail of hydrocarbon and sulfide gases in rising, mineral-rich formation water kills the microbiotic symbionts that are essential to plant root systems for nutrient uptake die and so too do trees. The onshore Solway Basin of Carboniferous age in NW England illustrates both points, having many chalybeate springs as the sulfide- and iron-rich waters are euphemistically known and also a strange phenomenon in many of the deep valleys cut by glacial melt waters as land rose following the last glacial maximum. Once trees reach a certain height – and correspondingly deep root systems – they die, to litter the valley woodland with large dead-heads.  Also leaves on smaller trees turn to their autumnal colours earlier than on higher ground. Both seem to be due to minor gas seepages from thick sale sequences in the depths of the sedimentary basin. Indeed, both are botanical indicators to the hydrocarbon explorationist.

To recap, a common size of a fracking operation using several horizontal wells driven from a single wellhead is 4km in diameter entering gas-rich shales at up to 2 km depth. Each well can generate fractures of a hundred metres or more in the shales and surrounding rocks, as they have to for commercial production. In Britain, most of the sites underlain by shales with gas potential are low-lying agricultural- or urban land. The producing rock in the Blackpool area is the Middle Carboniferous Bowland Shale that lies beneath the Coal Measures of what was formerly the Lancashire coalfield, now a patchwork of expanding urban centres. On 23 May 1984 an explosion occurred in Abbystead, Lancashire at an installation designed to pump winter flood water between the rivers Lune and Wyre through a tunnel beneath the Lower to Middle Carboniferous Bowland Fells. The Abbystead Disaster coincided with an inaugural demonstration of the pumping station to visitors, of whom 16 were killed and 22 injured. Methane had escaped from Carboniferous shales to build up in the flood-balancing  tunnel soon after its construction. Methane build-ups were by far the worst hazard throughout the history of British coal mining, thousands dying and being maimed as a result of explosions. One of the largest death tolls in British coal-mining history was 344 miners at Hulton Colliery in Westhoughton, Lancashire in 1910 after a methane explosion; the methane may well have escaped from the underlying Bowland Shales.

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Britain to be comprehensively fracked?

Tower for drilling horizontally into the Marce...

Drill rig in Pennsylvania aimed at hydraulic fracturing of the hydrocarbon-rich Marcellus Shale of Devonian age. Image via Wikipedia

In ‘Fracking’ shale and US ‘peak gas’ (EPN of 1 July 2010) I drew attention to the relief being offered to dwindling US self-sufficiency in natural gas by new drilling and subsurface rock-fracturing technologies that opens access to extremely ‘tight’ carbonaceous shale and the gas it contains. The item also hinted at the down-side of shale-gas. The ‘fracking’ industry has grown at an alarming rate in the USA, now supplying more than 20% of US demand for gas. This side of the Atlantic the once vast reserves of North Sea gas fields are approaching exhaustion. This is at a time when commitments to reducing carbon emissions dramatically depend to a large extent on hydrocarbon gas supplanting coal to generate electricity, releasing much lower CO2  by burning hydrogen-rich gases such as methane (CH4) than by using coal that contains mainly carbon. Without alternative, indigenous supplies declining gas reserves in Western Europe also seem likely to enforce dependency on piped gas from Russia or shipment of liquefied petroleum gas from those major oil fields that produce it. The scene has been set in Europe in general and Britain in particular for a massive round of exploration aimed at alternative gas sources beneath dry land. Unlike the US and Canada, the British are not accustomed to on-shore drilling rigs, seismic exploration and production platforms, and nor are most Europeans. Least welcome are the potential environmental and social hazards that have been associated with the US fracking industry, which seem a greater threat in more densely populated Europe.

The offshore oil and gas of the North Sea fields formed by a process of slow geothermal heating of solid hydrocarbons or kerogen in source rocks at a variety of stratigraphic levels, escape into surrounding rocks of the gases and liquids produced by this maturation, and their eventual migration and accumulation in geological traps. By no means all products of maturation leave shale source rocks because of their very low permeability. That residue may be much more voluminous than petroleum liquids and gases in conventional reservoir rocks; hence the attraction of fracking carbonaceous shales. British on-shore geology is bulging with them, particularly Devonian and Carboniferous lacustrine mudstones, Carboniferous and Jurassic coals, and the marine black shales of the Jurassic (see http://www.bgs.ac.uk/research/energy/shaleGas.html and https://www.og.decc.gov.uk/upstream/licensing/shalegas.pdf), to the extent that areas of potential fracking cover around a third of England, Wales and southern Scotland.

News is breaking of a major shale-gas discovery beneath Blackpool, the seaside resort ‘noted for fresh air and fun, where Mr and Mrs Ramsbottom went with Young Albert their son…’ (Albert poked a stick at Wallace the lion and was eaten), said by energy firm Cuadrilla to have gas reserves of 5.7 trillion m3. The announcement followed 6 months of exploratory drilling, and drew attention to the burgeoning interest by entrepreneurs in the upcoming 14th Onshore Licensing Round for petroleum exploration in Britain. It isn’t just from major petroleum companies, but in some cases even what amount to family businesses finding sufficient venture capital to spud wells; similar in many respects to the US fracking boom that began a mere 10 years ago.