Shale oil is produced from a subterranean interval of oil shale, where the interval is initially substantially impermeable and contains a specified grade and thickness of oil shale. Said interval is conductively heated from borehole interiors which are kept hotter than about 600.degree. C. and are heated...http://www.google.de/patents/US4886118?utm_source=gb-gplus-sharePatent US4886118 - Conductively heating a subterranean oil shale to create permeability and subsequently produce oil
