Shale pits environmental versus economic interests

Shale oil and gas may be massive untapped energy sources, but the risks of extracting them has drawn calls for tighter regulation or an all-out ban. To release oil or natural gas locked inside sedimentary shale rock, energy companies inject at high pressure a mixture of water, sand and chemicals deep underground to crack the layer (sometimes called source rock) where the hydrocarbons lurk. The technology, known as hydraulic fracturing or "fracking," is typically used at depths of 2,000 to 4,000 metres (6,500 to 13,000 feet) below the earth's surface. The fracking mixture is then partially pumped back up. Environmentalists have warned gas, mostly methane, or some of the remaining injected mix can eventually rise toward the surface on its own, polluting fresh-water supplies. But geologists interviewed by AFP downplayed that risk, saying the cracks formed by fracking are generally more than 1,000 metres below the water table, with thick layers of rock in between keeping aquifers safe. Only one controversial draft study in 2011 by the US Environmental Protection Agency found evidence of ground-water contamination linked to fracking in the town of Pavillion, Wyoming. But EPA officials dropped their probe in June and handed it over to local authorities without drawing final conclusions.