Recovery of petroleum by combination reverse-direct in situ combustion

Claim 1

IN A PROCESS FOR THE UNDERGROUND COMBUSTION OF A CARBONACEOUS DEPOSIT SELECTED FROM THE GROUP CONSISTING OF PETROLEUM TARS AND HEAVY VISCOUS OILS, SAID DEPOSIT BEING PENETRATED AT SPACED POINTS BY AN INJECTION AND A PRODUCING WELL, THE IMPROVEMENT WHICH COMPRISES INJECTING INTO SAID DEPOSIT VIA SAID INJECTION WELL AN OXYGEN-CONTAINING GAS, INTITIATING A COMBUSTION ZONE AT A POINT IN SAID DEPOSIT REMOTE FROM SAID INJECTION WELL, SAID POINT NOT EXCEEDING THE DISTANCE BETWEEN SAID WELLS AND FALLING SUBSTANTIALLY ON A LINE CONNECTING SAID WELLS, THEREAFTER SUPPLYING AN OXYGEN-CONTAINING GAS THROUGH SAID INJECTION WELL TO SAID ZONE TO MAINTAIN SAID ZONE AND TO PROPAGATE IT THROUGH SAID DEPOSIT TOWARD SAID INJECTION WELL UNTIL SAID ZONE HAS REACHED AT LEAST THE IMMEDIATE AREA OF SAID INJECTION WELL, CONTROLLING THE TEMPERATURE AT A GIVEN OXYGEN-CONTAINING GAS FLUX OF SAID COMBUSTION ZONE WHILE THE LATTER IS MOVING TOWARD SAID INJECTION WELL BY MEANS OF REGULATING THE RESERVOIR PRESSURE, SUBSEQUENTLY INTRODUCING AN OXYGENCONTAINING GAS INTO SAID DEPOSIT VIA SAID INJECTION WELL WHEREBY THE COURSE OF SAID ZONE IS REVERSED AND TRAVELS CONCURRENTLY WITH SAID GAS TOWARD SAID PRODUCING WELL, AND RECOVERING FLUID THROUGH SAID PRODUCING WELL RESULTING FROM THE CONCURRENT TRAVEL OF SAID GAS AND COMBUSTION ZONE.