Intermittent direct in situ burning method

Claim 1

IN A METHOD OF RECOVERING HYDROCARBONS BY INTERMITTENT IN SITU COMBUSTION FROM A SUBTERRNAEAN OIL-BEARING FORMATION WHICH HAS BEEN PENETRATED BY AN INPUT WELL AND AN ADJACENT PRODUCTION WELL AND INCLUDES THE STEPS OF INITIATING A COMBUSTION ZONE IN A PORTION OF THE OILBEARING-FORMATION ADJACENT THE INPUT WELL AND INJECTING AN OXYGEN-CONTAINING FLUID INTO THE COMBUSTION ZONE TO DRIVE A COMBUSTION FRONT THROUGH THE MORE PERMEABLE AREAS OF THE OIL-BEARING FORMATION TO THE PORDUCTION WELL, RECOVERING HYDROCARBONS FROM THE PRODUCTION WELL, TERMINATING THE INJECTION OF THE OXYGEN-CONTAINING FLUID INTO THE FORMATION UPON THE PRODUCTION WELL BEING HEATED TO ABOUT WELL-DESTRUCTIVE TEMPERATURE FOR AN INTERVAL OF TIME UNTIL THE FORMATION ADJACENT THE PRODUCTIN WELL COOLS TO A TEMPERATURE AT WHICH THE FORMATION OIL IS TOO VISCOUS TO BE PRODUCED IN SIGNIFICANT AMOUNTS AND THEREAFTER REPEATING THE RECITED STEPS, THE IMPROVEMENT WHICH COMPRISES INJECTING A HYDROCARBON-SOLUBLE GAS THROUGH THE INPUT WELL TO INCREASE THE GAS-TO-OIL RATIO OF THE UNBURNED OIL-BEARING FORMATION AND THE COMBUSTION ZONE BETWEEN THE INPUT AND PRODUCTION WELLS FOR THE INTERVAL OF TIME WHEN THE INJECTION OF THE OXYGEN-CONAINING FLUID IS TERMINATED WHEREBY THE HEAT FROM THE COMBUSTION ZONE IS DISTRIBUTED TO THE UNBURNED OIL-BEARING FORMATION AND THE VISCOSITY OF THE OIL IN SUCH FORMATION IS REDUCED.