Underground combustion process

Claim 1

IN A PROCESS FOR THE UNDERGROUND COMBUSTION OF A CARBONACEOUS DEPOSIT, SAID DEPOSIT BEING PENETRATED AT SPACED POINTS BY AN INJECTION WELL AND A PRODUCING WELL, THE IMPROVEMENT WHICH COMPRISES INJECTING INTO SAID DEPOSITS AN OXYGEN-CONTAINING GAS, INITIATING A ZONE OF COMBUSTION IN SAID DEPOSIT AT A POINT ADJOINING SAID PRODUCING WELL, SUBJECTING SAID DEPOSIT TO A PRESSURE OF FROM ABOUT 100 P.S.I. TO A PRESSURE JUST BELOW THAT REQUIRED TO FRACTURE SAID DEPOSIT, THEREAFTER SUPPLYING AN OXYGEN-CONTAINING GAS THROUGH SAID INJECTION WELL TO 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 AN AREA ADJACENT A SAID INJECTION WELL, THEREAFTER INJECTING A FLUID OF THE TYPE DEFINED INTO ONE OF SAID WELLS, SAID FLUID BEING INJECTED IN AN AMOUNT INSUFFICIENT TO INTERFERE WITH THE TEMPERATURE PREVAILING IN THE BURNED AREA BETWEEN SAID WELLS, NEXT INTRODUCING AN OXYGEN-CONTAINING GAS INTO SAID DEPOSIT THROUGH ONE OF SAID WELLS, WHILE THE FACE OF SAID DEPOSIT AT SAID ONE OF SAID WELLS IS SUBSTANTIALLY AT COMBUSTION TEMPERATURE, CONTINUING THE INTRODUCTION OF SAID GAS, AND RECOVERING THE RESULTING VALUABLE PRODUCTS FROM THE OTHER OF SAID WELLS.