In situ combustion

Claim 1

A METHOD OF CARRYING OUT AN IN SITU COMBUSTION OPERATION FOR THE PRODUCTION OF HYDROCARBONS FROM AN UNDERGROUND FORMATION CONTAINING VISCOUS CRUDE OIL HAVING AN API GRAVITY LESS THAN 30* WHICH COMPRISES INITIATING IN SITU COMBUSTION WITHIN SAID FORMATION IN A ZONE ADJACENT A FIRST WELL BORE PENETRATING SAID FORMATION, INTRODUCING AIR INTO SAID FORMATION VIA SAID FIRST WELL BORE TO MAINTAIN IN SITU COMBUSTION THEREIN TO REDUCE THE VISCOSITY OF SAID CRUDE OIL AND TO DISPLACE HYDROCARBONS OF REDUCED VISCOSITY FROM SAID FORMATION TOWARD A SECOND WELL BORE PENETRATING SAID FORMATION AT A DISTANCE REMOVED FROM SAID FIRST WELL BORE, PRODUCING THE RESULTING DISPLACED HYDROCARBONS FROM SAID FORMATION VIA SAID SECOND WELL BORE, DISCONTINUING THE INJECTION OF SAID COMBUSTION SUPPORTING GAS INTO SAID FORMATION VIA SAID FIRST WELL BORE, INTRODUCING INTO SAID FORMATION VIA SAID FIRST WELL BORE A NON-COMBUSTION SUPPORTING GAS AS A HEAT CARRIER TO TRANSFER THE HEAT FROM THE HIGH TEMPERATURE COMBUSTION ZONE CREATED WITHIN SAID FORMATION TO ANOTHER PORTION OF SAID FORMATION ADJACENT SAID HIGH TEMPERATURE COMBUSTION ZONE IN THE DIRECTION OF SAID SECOND WELL BORE AND IN THE DIRECTION OF THE FLOW OF SAID NON-COMBUSTION SUPPORTING GAS WITHIN SAID FORMATION WHEREBY THE HYDROCARBONS IN SAID OTHER PORTION OF THE FORMATION ARE HEATED TO A RELATIVELY ELEVATED TEMPERATURE TO EFFECT VISCOSITY REDUCTION, DISCONTINUING THE INJECTION OF SAID NON-COMBUSTION SUPPORTING GAS INTO SAID FORMATION VIA SAID FIRST WELL BORE, INTRODUCING AIR INTO SAID FORMATION VIA SAID SECOND WELL BORE TO INITIATE AND/OR MAINTAIN IN SITU COMBUSTION IN THE PRESENCE OF HYDROCARBONS WITH REDUCED VISCOSITY WITHIN SAID FORMATION IN SAID OTHER PORTION OF SAID FORMATION UNDER CONDITIONS SUCH THAT THE HIGH TEMPERATURE COMBUSTION ZONE WITHIN SAID FORMATION RESULTING FROM SAID IN SITU COMBUSTION MOVES WITHIN SAID FORMATION IN THE DIRECTION OF SAID SECOND WELL BORE AND COUNTERCURRENT TO THE FLOW OF SAID COMBUSTION SUPPORTING GAS INTRODUCED INTO SAID FORMATION VIA SAID SECOND WELL BORE AND PRODUCING THE RESULTING DISPLACED HYDROCARBONS OF REDUCED VISCOSITY FROM SAID FORMATION VIA SAID FIRST WELL BORE.