Flaming rocks

摘要

The cliffs at Kimmeridge, on England's south coast, have on occasions been known to smoulder or even burst into flames in hot weather. That is because, unlike the famous white chalk cliffs of Dover, they are made of oil shale, a soft rock that has hydrocarbons trapped in its pores. The world's oil-shale beds may contain the equivalent of up to nine times as much oil as all of its conventional wells. Confusingly, oil shale has nothing to do with fracking, a technique for extracting oil and gas from a different sort of shale through horizontal drilling and hydraulic fracturing. America is blessed with prodigious quantities of both types of shale. Its fracking pioneers have successfully exploited one type, transforming the country's energy supply. But hitherto, squeezing the energy out of oil shale has generally proved uneconomic, and even more environmentally unsound than other forms of fossil-fuel extraction.