On Wednesday this week (2 November 2011) a report commissioned by petrochemical exploration company Cuadrilla Resources concluded that experimental hydraulic fractionation (fracking) carried out by the company at a site near Blackpool on the Lancashire coast had been responsible for two small earthquakes in the region in April and May this year, something they had been accused of by environmental protestors. The company suspended operations at the site after the second quake, but resumed during the summer. This week the site was occupied by environmental group Frack Off, causing another suspension of activity.
A Cuadrilla drilling rig in Lancashire.
Hydraulic fractionation is a process by which pressurized gas, water or other chemicals are forced into brittle, impermeable rock believed to contain gas reserves, in this case the Bowland Shale, fracturing the rock to release the gas. In this sense the whole purpose of the process is to cause earthquakes, though not as large as the ones produced in Lancashire. Ideally the process would produce quakes with magnitudes of less than one on the Richter Scale, the quakes recorded this spring near Blackpool had magnitudes of 2.3 and 1.5 respectively; hardly devastating, but since they were quite shallow, widely felt in this populous region. Numerous smaller quakes were also detected by seismometers, but not noticed by the local population. This is unusual but not unprecedented; fracking operations on the Eola Field in Oklahoma have produced quakes with magnitudes of up to 2.8, and the process has been linked to similar sized tremors in Texas.
The report cites 'unusual geology' around the site as the cause of the unexpectedly large quakes, though this seems a little disingenuous; a company like this would normally be expected to study the geology at a site like this before beginning operations. The report concludes that the operation is unlikely to cause earthquakes with magnitudes of greater than 3, not enough to present a danger to the public and less than produced by some mining activities, particularly those involving blasting. This is unlikely to be reassuring to residents of the region; what the report is effectively saying is that they did not expect the fracking to cause quakes big enough to be noticed, but now that they have done so they do not expect to produce quakes big enough to be dangerous.
In fairness it is difficult to see how they could produce a quake much larger than this, even if they wanted to, without inputting a lot more energy. The Richter Scale is logarithmic, so that a magnitude 3 quake is 100 times as great as a magnitude 1 quake. A magnitude 4 quake (still unlikely to be dangerous) is 10 times as large again, i.e. over a thousand times larger than the quakes they would be trying to cause (with a magnitude of less than one). However this is not quite the point. The people of Lancashire have effectively found they are now living above an artillery firing range; it may not be actually dangerous, but it remains to be seen if they will accept this happily, and if not whether they will be able to do anything about it.
Environmentalists are widely opposed to fracking for reasons other than earthquakes. Firstly they are generally opposed to increasing hydrocarbon exploration, since burning fossil fuels increases the level of CO₂ in the atmosphere, leading to climate change. Secondly, and more specifically, fracking has been linked to the release of other chemicals trapped within strata, contaminating groundwater with toxic and carcinogenic hydrocarbons.
Hydraulic fractioning is currently banned in France for environmental reasons. There are also temporary moratoria in place in South Africa, New South Wales, Quebec and New York State.
This week also sees a summit on shale gas production in London, which is likely to determine the future of the industry in the UK. There is a great deal of potential for the expansion of the industry, particularly in northern England, with some shale gas deposits in the Midlands, northern Wales and southern Scotland. The UK's current government is likely to be favorable to expansion of the industry, with a number of ministers who apparently see all environmental legislation as unnecessary 'red tape', but it is also likely that public opposition to the process will be strong, particularly if it becomes associated in the public's eyes with earthquakes.
Maps showing the location of ancient turbidite deposits in Britain, with the areas thought to contain shale gas deposits in green. Turbidites are deposits caused by massive submarine landslips, which sweep thousands of tonnes of sediment and associated lifeforms into the deep ocean. Over time these lifeforms decay, releasing methane gas which becomes trapped in the sediments. The deposits all date from the Carboniferous, with the oldest from the Arundian being about 345 million years old and the youngest from the Early Namurian being about 325 million years old.