Thermal recovery of heavy crude oil

Claim 1

A PROCESS FOR PRODUCING FLUID HYDROCARBONS FROM A SUBTERRANEAN STRATUM HAVING SUBSTANTIAL PRESSURE, CONTAINING A VISCOUS CRUDE OIL, AND BEING PENETRATED BY FIRST AND SECOND WELLS WHICH COMPRISES THE STEPS OF: (1) INJECTING AIR THRU SAID FIRST WELL INTO SAID STRATUM WHILE MAINTAINING SAID SECOND WELL SHUT-IN SO AS TO DRIVE BEYOND SAID SECOND WELL HYDROCARBON FLUIDS IN SAID STRATUM MOBILE UNDER THE CONDITIONS THEREIN TO FORM A PARTIALLY EVACUATED SECTION INTERMEDIATE SAID WELLS; (2) THEREAFTER, TERMINATING INJECTION THRU SAID FIRST WELL AND INJECTING AIR THRU SAID SECOND WELL AND PRODUCING FLUIDS THRU SAID FIRST WELL UNDER BACKPRESSURE SUBSTANTIALLY EQUAL TO STRATUM PRESSURE IN THE AIR INJECTION AREA SO AS TO PREVENT INVASION OF DISPLACED FLUIDS INTO SAID PARTIALLY EVACUATED SECTION; (3) AFTER STEP (2) HAS EFFECTED AN AIR-LIQUID RATIO OF AT LEAST 30M S.C.F./BBL., IGNITING SAID STRATUM ADJACENT AID FIRST WELL WHILE STILL UNDER SAID BACKPRESSURE TO ESTABLISH A COMBUSTION ZONE; (4) CONTINUING INJECTION OF AIR IN STEP (2) SO AS TO MOVE SAID COMBUSTION ZONE COUNTERCURRENTLY TO AIR FLOW TOWARD SAID SECOND WELL; (5) AFTER SAID COMBUSTION ZONE HAS BEEN MOVED A SUBSTANTIAL PORTION OF THE DISTANCE TO SAID SECOND WELL, DECREASING THE BACKPRESSURE ON SAID FIRST WELL BELOW STRATUM PRESSURE IN THE INJECTION AREA SO AS TO ALLOW DISPLACED HYDROCARBON FLUIDS TO FLOW INTO THE COMBUSTION ZONE AND THE HOT BURNED OVER AREA BEHIND SAID ZONE AND CONTINUING THE INJECTION OF AIR AS IN STEP (4) SO AS TO BURN A PORTION OF THE INVADING HYDROCARBON FLUIDS AND PRODUCE A PORTION THEREOF AS LIGHTER HYDROCARBONS; AND (6) RECOVERING PRODUCED HYDROCARBON FLUIDS FROM SAID FIRST WELL.