Recovery of hydrocarbon materials from earth formations by application of heat

Claim 1

IN A PROCESS FOR THE RECOVERY OF HYDROCARBON MATERIALS FROM AN EARTH FORMATION WHEREIN AN OXIDIZING GAS IS PASSED TO SAID FORMATION THROUGH AN INPUT WELL LEADING THERETO AND FORCED THROUGH SAID FORMATION TO AT LEAST ONE OUTPUT WELL LEADING THEREFROM, COMBUSTION OF A PORTION OF THE HYDROCARBON MATERIALS IS MAINTAINED WITHIN SAID FORMATION, AND A COMBUSTION ZONE IS ADVANCED THROUGH SAID FORMATION AS A RESULT OF THE PASSAGE OF SAID OXIDIZING GAS, THE IMPROVEMENT COMPRISING PASSING OF SAID OXIDIZING GAS TO SAID FORMATION THROUGH SAID INPUT WELL IN THE DIRECTION OF SAID OUTPUT WELL UNTIL SAID COMBUSTION ZONE AS A RESULT OF THE PASSAGE OF SAID OXIDIZING GAS TO SAID FORMATION HAS ADVANCED MORE THAN 40 PERCENT BUT LESS THAN 90 PERCENT OF THE DISTANCE ON A STRAIGHT LINE BETWEEN SAID INPUT WELL AND SAID OUTPUT WELL, DISCONTINUING PASSAGE OF GAS THROUGH SAID INPUT WELL TO SAID FORMATION FOR A PERIOD OF TIME WHICH IS APPRECIABLE AND IS AT LEAST AS GREAT AS ONE MONTH THEREBY PERMITTING HEAT WITHOUT ASSISTANCE FROM INJECTION OF FLUID IN THE DIRECTION OF SAID OUTPUT WELL DURING SAID PERIOD OF TIME TO TRANSFER FROM THE PORTION OF SAID FORMATION TRAVERSED BY SAID COMBUSTION ZONE TO THE PORTION OF SAID FORMATION IN THE DIRECTION OF SAID OUTPUT WELL NOT TRAVERSED BY SAID COMBUSTION ZONE, AND THEREAFTER, TO ASSIST IN PRODUCTION OF HYDROCARBON MATERIALS FROM SAID OUTPUT WELL, PASSING FLUID THROUGH SAID FORMATION TO SAID OUTPUT WELL UNDER CONDITIONS THAT COMBUSTION OF SAID HYDROCARBON MATERIALS IN SAID FORMATION IS ABSENT.