Seismic Report Earthshaking?
In September, Cuadrilla Resources, the first company to drill for shale gas in Britain, estimated that 200 trillion cubic feet of gas lie in an area of Lancashire near Blackpool, in northwest England. On the basis of two well points in the area, it predicted that there were nearly 40 times the previous projections of all of Britain’s shale resources. It is likely that, even if accurate, only a small proportion of such reserves might actually be recoverable.
So far, so good. But there was a problem. In May, the company had to stop drilling because two tiny tremors were recorded in the region. These were so small—2.3 and 1.5 magnitude—that they would barely have been felt. Nonetheless, exploration was halted over concerns that the seismic activity had been caused by deep drilling and hydraulic fracturing or “fracking”, the process by which huge volumes of water are blasted through rock at high pressure in order to extract the gas. The company commissioned a report by a team of independent seismic experts.
That report, Geomechanical Study of Bowland Shale Seismicity, found that it was “highly probable” that Cuadrilla’s activity did cause the shocks. It reckons they were caused by an “unusual combination of geology at the well site coupled with the pressure exerted by fracking”. Mike Stephenson of the British Geological Survey says he is not surprised at the report’s conclusion that these shocks were connected to Cuadrilla’s activities—BGS’s analysis already showed that the shape of the seismic traces the two earthquakes made were similar to each other, suggesting that they had the same trigger.
One of Mr Stephenson's colleagues, Brian Baptie, also of the British Geological Survey, notes that magnitude does not always tell us everything that needs to be known. A shallow tremor of 2.6, for example, may cause quite strong and perceptible shaking indoors and out. He also points out that coal-mining caused a lot of small tremors in the 1970s and 1980s. These were monitored, but did not cause great problems.
Nevertheless, the findings about Cuadrilla's activity will certainly contribute to a prevailing anxiety about fracking. Poland is gung-ho about it and is happily exploring its own shale reserves. But France and two American states have temporarily halted fracking because of fears that chemicals used in the process may pollute water sources. Numerous studies have found that fracking is safe. But many groups are still anxious, and some oil and gas companies have been unhelpfully closed about exactly what chemicals they use.
The threat of seismic activity is distinct from these concerns. But it will, of course, add to concerns about exploiting shale gas. Unsurprisingly, WWF and Friends of the Earth, two environmental lobbies, have already used this report as a chance to repeat calls to leave shale gas in the ground while further studies are done of the potential risks. Both organisations also think money and effort should be put into developing renewable sources of energy, not searching for more carbon-emitting fossil fuels.
So this is certainly a set back for the shale publicity machine. Beyond that, there are real questions here for Cuadrilla. Compared to drilling for conventional natural gas, shale extraction requires digging many more wells to get at the gas. Cuadrilla has already said it wants to drill at 400 sites in Lancashire. If fracking at one well can cause two small shocks, that must raise concerns about what fracking at 400 points would do. The shale reserves in this area are also much deeper than equivalent areas in America, the company reckons, though Mr Baptie says this doesn't neccessarily affect any likelihood of seismic activity.
Today’s report says the combination of geological factors was “extremely rare and would be unlikely to occur together again at future well sites”. The British Geological Survey's Mr Baptie points out, though, that the geology in the area around the first well is likely to be quite similar. A 2.3 magnitude tremor can be triggered on a fault 100 metres in diameter which moves by just 1cm, he says — and that sort of geology "might be difficult to identify".
It’s interesting to note that in the Netherlands, large, on-land gas reservoirs have been exploited since 1960. This extraction has also caused repeated small magnitude (less than 3.5), shallow shocks which caused light damage—but much concern—to the regional population. Nevertheless, that seismic activity did not stop the extraction, or any other activity, in that area.
Another example, less useful to Cuadrilla, was seen in the geothermal industry in Basel in Switzerland in 2006. A warning system was put in place to monitor seismic activity, just as Cuadrilla is likely to install. When a number of events of magnitudes greater than two were recorded, the projects stopped. Yet they weren't halted soon enough—a larger tremor of magnitude 3.5 was recorded, after other operations had ceased.
It would be more than unfortunate to turn Britain into an earthquake zone. But these quakes really are extremely small. Does it matter if a small shudder, equivalent to a tube train running underground, runs through the earth? The question is whether a broad area of deep drilling and fracking might cause any bigger earthquakes. If fracking is allowed to go ahead in this area, Cuadrilla is sure to be asked to note not just how many tremors are felt, but how often and whether they are getting bigger. Exploration companies have been pulling oil and gas from the bowels of the earth for decades. There have certainly been catastrophic disasters—but not seismic ones.
Whether shale gas extraction is now allowed to go to the next stage of exploration in Britain will depend on the Department for Energy and Climate Change. For advocates, shale gas is the "wonder gas" of the future. But some questions remain to be answered.
Source: The Economist
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