Serially burning and pyrolyzing to produce shale oil from a subterranean oil shale

In a process for producing shale oil from a subterranean oil shale formation that contains water-soluble material by forming a cavity within the oil shale formation, leaching water-soluble mineral to form a permeable oil shale rubble within the cavity, and circulating hot fluid through the cavity to pyrolyze the permeable oil shale rubble and recover shale oil, the improvement which comprises:

• forming at least two cavities;
• leaching water-soluble minerals by circulating aqueous liquid which is hotter than the surrounding oil shale through at least two cavities to form a relatively hot permeable oil shale rubble in each cavity;
• initiating an underground combustion and advancing a combustion front through at least one cavity containing a permeable oil shale rubble or a pyrolyzed oil shale rubble that contains carbonaceous material;
• circulating hot combustion products composed mainly of the oxides of carbon, hydrogen and nitrogen formed by said underground combustion through the permeable oil shale rubble in at least one of said cavities;
• and
• recovering shale oil from at least one fluid produced from at least one of said cavities.