Tham Min Jack, Closmann Philip Joseph: Solvent/non-solvent pyrolysis of subterranean oil shale. Shell Oil Company, Coryell Harold W, April 29, 1975: US3880238 (29 worldwide citation)

In a process for recovering shale oil by injecting and producing fluid into and out of a rubble-containing cavity in an otherwise substantially impermeable subterranean oil shale, the tendency for the flow path to become plugged is reduced by injecting both a hot solvent-fluid and a non-solvent-gas ...

Knapp Randolph H: Asphalt plug emplacement process. Shell Oil Company, Coryell Harold W, August 26, 1975: US3901316 (19 worldwide citation)

A process for plugging a subterranean earth formation by injecting an asphalt-containing emulsion is improved by a cationic emulsifier and a pH increasing reactant that induces the breaking of the emulsion in response to a time-temperature exposure of selected extent.