1
Garret Donald E: In situ process for recovery of carbonaceous materials from subterranean deposits. Occidental Petroleum Corporation, May 9, 1972: US3661423 (350 worldwide citation)

Subterranean carbonaceous deposits, such as oil shale, are conditioned for in-situ recovery of carbonaceous values by limited undercutting over a large area to leave an overlaying deposit supported by a multiplicity of pillars, if necessary, then removing the pillars and expanding the overlaying dep ...


2
Wilmer A Hoyer: In situ process for recovery of carbonaceous materials from subterranean deposits. Exxon Production Research Company, Gary D Lawson, Michael A Nametz, May 30, 1978: US04091869 (235 worldwide citation)

A method is disclosed for recovering carbonaceous material from a subterranean deposit such as oil shale. A first zone of the subterranean deposit is heated to liquefy and vaporize carbonaceous materials contained therein. A substantial portion of the carbonaceous materials are removed from this fir ...