Solvent/non-solvent pyrolysis of subterranean oil shale

Claim 1

A SHALE OIL-PRODUCING PROCESS IN WHICH A RUBBLECONTAINING CAVERN IS FORMED WITHIN AN OTHERWISE SUBSTANTIALLY IMPERMEABLE SUBTERRANEAN OIL SHALE THAT CONTAINS WATERSOLUBLE MINERALS AND FLUID IS INJECTED INTO AND WITHDRAWN FROM THE CAVERN, THE IMPROVEMENT WHICH COMPRISES: IN AN UPPER PORTION OF SAID CAVERN, INJECTING HOT SOLVENTFLUID HAVING A SIGNIFICANT MISCIBILITY WITH AT LEAST ONE ORGANIC OR INORGANIC SOLID OR LIQUID PYROLYSIS PRODUCT OF SAID OIL SHALE; IN AN UPPER PORTION OF SAID CAVERN, INJECTING HOT NONSOLVENT-GAS HAVING A RELATIVELY INSIGNIFANT MISCIBILITY WITH ANY OF THE ORGANIC OR INORGANIC SOLID OR LIQUID PYROLYSIS PRODUCTS OF SAID OIL SHALE; WITHDRAWING FLUID FROM SAID CAVERN FROM A LEVEL BELOW ANY AT WHICH FLUID IS INJECTED INTO THE CAVERN; CORRELATING THE PROPERTIES AND FLOW RATES OF THE INFLOWING AND OUTFLOWING PORTIONS OF SAID FLUIDS SO THAT THE CAVERN REMAINS SUFFICIENTLY LIQUID-FREE TO PREVENT A SIGNIFICANT PLUGGING OF THE FLUID FLOW PATH; AND RECOVERING A SHALE OIL FROM FLUID WITHDRAWN FROM SAID CAVERN.