Method of reversing in situ combustion frontal movement

Claim 1

A PROCESS FOR THE UNDERGROUND COMBUSTION OF A GAS PREVIOUS CARBONACEOUS DEPOSIT PENETRATED AT SPACED POINTS BY AN INJECTION WELL AND A PRODUCTION WELL WHICH COMPRISES INITIATING A ZONE OF COMBUSTION THEREIN AT A POINT ADJOINING SAID PRODUCTION WELL BY HEATING AND CONTACTING THE DEPOSIT AT SAID POINT WITH AN O2-CONTAINING GAS; THEREAFTER SUPPLYING O2-CONTAINING GAS (AT LESS THAN COMBUSTION SUPPORTING TEMPERATURE AT THE AREA OF INJECTION) THRU SAID INJECTION WELL TO SAID ZONE TO MAINTAIN SAID ZONE AND TO PROPAGATE SAME INTO SAID DEPOSIT AWAY FROM SAID PRODUCTION WELL COUNTERCURRENTLY TO THE FLOW OF SAID GAS; AFTER SAID ZONE HAS BEEN MOVED SUBSTANTIALLY AWAY FROM SAID PRODUCTION WELL, AND, WHILE IT IS SPACED SUBSTANTIALLY FROM SAID INJECTION WELL, REVERSING THE DIRECTION OF MOVEMENT THEREOF BY REDUCING THE O2 FLOW RATE TO SAID ZONE BELOW A SUSTAINING RATE FOR AN INVERSE BURNING ZONE, AND DRIVING SAME BACK TOWARD SAID PRODUCTION WELL BY INJECTING O2-CONTAINING GAS TO SAID ZONE; AND RECOVERING FLUIDS RESULTING THEREFROM THRU SAID PRODUCTION WELL.