9th
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, came out today, and 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”.
Gas extraction: Shale shocked | The Economist
英国のランカシャーでシェールガス田開発由来と考えられる地震があったそうだ。これは、この記事にリンクされている調査レポートを読むと、シェールガスを掘削するのに水平方向に超高圧水流で岩盤を掘り進むのだが、普通のドリルによる垂直掘りに比べて地下の構造を大きな領域に渡って変えてしまうかららしい。
これにより、環境ロビー団体もメシのタネを見つけたということで、夢の資源と言われているシェールガス田開発に少し暗雲がかかってくるかもしれないそうだ。