In situ combustion process

Claim 1

A PROCESS FOR PRODUCING HYDROCARBONS FROM A PLURALITY OF READILY COMBUSTIBLE UNDERGROUND OIL-BEARING LAYERS RANGING FROM RELATIVELY HIGH TO RELATIVELY LOW NATURAL PERMEABILITY, WHEREIN EACH PAIR OF ADJACENT LAYERS IS SEPARATED BY A RELATIVELY THIN IMPERMEABLE LAYER, WHICH COMPRISES SEPARATELY PRODUCING A LAYER OF HIGH PERMEABILITY BY IGNITING A SECTION THEREOF AROUND A WELL THEREIN, FEEDING O2-CONTAINING COMBUSTION-SUPPORTING GAS TO THE IGNITED ZONE, AND CONTINUING THE INJECTION OF SAID GAS SO AS TO MOVE SAID ZONE TO ANOTHER WELL THEREIN, WHEREBY AT LEAST ONE ADJACENT LESS PERMEABLE LAYER IS HEATED SO AS TO REDUCE THE VISCOSITY OF HYDROCARBONS THEREIN; THEREAFTER, WHILE SAID ADJACENT LAYER IS HOT, PRODUCING SAME BY GAS DRIVE INCLUDING INJECTING A RELATIVELY INERT NON-HYDROCARBON GAS CONTINUOUSLY THROUGH ONE OF SAID WELLS INTO SAID LESS PERMEABLE LAYER AND PRODUCING GAS AND HYDROCARBONS THROUGH THE OTHER WELL, THEREBY INCREASING THE PERMEABILITY THEREOF; AND PRODUCING LAST SAID LAYER BY IN SITU CONBUSTION INCLUDING IGNITING LAST LAYER AROUND ONE OF SAID WELLS AND INJECTING COMBUSTION-SUPPORTING GAS INTO THE IGNITED AREAA THROUGH ONE OF SAID WELLS SO AS TO PRODUCE HYDROCARBONS THROUGH THE OTHER WELL.