Secondary recovery of oil from a subterranean formation

Claim 1

IN A METHOD OF RECOVERING OIL FROM A SUBTERRANEAN RESERVOIR PENETRATED BY AT LEAST ONE INJECTION WELL AND ONE PRODUCTION WELL, SAID WELLS BEING SPACED APART ONE FROM THE OTHER, THE STEPS WHICH COMPRISE: (A) INTRODUCING CARBON DIOXIDE INTO SAID RESERVOIR THROUGH SAID INJECTION WELL, AND DRIVING SAID CARBON DIOXIDE THROUGH SAID RESERVOIR, INTO CONTACT WITH SAID OIL, SAID CARBON DIOXIDE BEING INTRODUCED INTO SAID RESERVOIR IN AN AMOUNT TO PROVIDE WITHIN SAID RESERVOIR A FIRST TRANSITION ZONE, SAID FIRST TRANSITION ZONE INCLUDING A PORTION NEXT TO SAID OIL WHICH IS A MIXTURE OF SAID CARBON DIOXIDE AND SAID OIL, AND A CARBON DIOXIDE PHASE FOLLOWING SAID MIXTURE OF SAID CARBON DIOXIDE AND SAID OIL; (B) INTRODUUCING A LIQUUEFIED HYDROCARBON MATERIAL INTO SAID RESERVOIR THROUGH SAID INJECTION WELL, AND DRIVING SAID LIQUEFIED HYDROCARBON MATERIAL THROUGH SAID RESERVOIR, BEHIND AND INTO CONTACT WITH SAID CARBON DIOXIDE PHASE, SAID LIQUEFIED HYDROCARBON MATERIAL BEING INTRODUCED INTO SAID RESERVOIR AT A PRESSURE WHICH WILL MAINTAIN SAID LIQUEFIED HYDROCARBON MATERIAL IN THE LIQUEFIED STATE IN SAID RESERVOIR TO PROVIDE WITHIN SAID RESERVOIR NEXT TO SAID CARBON DIOXIDE PHASE A SECOND TRANSITION ZONE, SAID SECOND TRANSITION ZONE INCLUDING A PORTION WHICH IS A MIXTUURE OF SAID CARBON DIOXIDE AND SAID LIQUEFIED HYDROCARBON MATERIAL, AND A ZONE OF SAID LIQUEFIED HYDROCARBON MATERIAL WHEREBY SAID FIRST TRANSITION ZONE, SAID CARBON DIOXIDE PHASE, AND SAID SECOND TRANSITION ZONE PROVIDE A SMOOTH VISCOSITY TRANSITION FROM SAID OIL TO SAID ZONE OF LIQUEFIED HYDROCARBON MATERIAL; (C) INTRODUCING INTO SAID RESERVOIR THROUGH SAID INJECTION WELL A DRIVING FLUID TO DISPLACE SAID OIL, SAID TRANSITION ZONES, SAID CARBON DIOXIDE PHASE, AND SAID LIQUEFIED HYDROCARBON MATERIAL THROUUGH SAID RESERVOIR TOWARD SAID PRODUCTION WELL; AND (D) PRODUUCING SAID OIL FROM SAID RESERVOIR THROUGH SAID PRODUCTION WELL.