A subterranean formation containing oil shale is prepared for in situ retorting by initially excavating a pair of spaced apart voids, leaving an intervening zone of unfragmented formation between the voids. The intervening zone has substantially parallel free faces adjoining the void. A plurality of...http://www.google.es/patents/US4146272?utm_source=gb-gplus-sharePatente US4146272 - Explosive placement for explosive expansion toward spaced apart voids
Explosive placement for explosive expansion toward spaced apart voids
