Method and apparatus for injecting steam into subsurface formations

Claim 1

IN AN OIL-BEARING FORMATION TRAVERSED BY AN INJECTION WELL AND A PRODUCING WELL IN COMMUNICATION WITH THE SAME FORMATION, AND WHEREIN SAID INJECTION WELL IS EQUIPPED WITH A CEMENTED WELL CASING IN OPEN FLUID COMMUNICATION WITH THE OIL FORMATION AND AN INTERMEDIATE CONCENTRIC PIPE STRING AND AN INNER TUBING STRING WITHIN THE CASING FORMING INNER AND OUTER ANNULAR SPACES EXTENDING SUBSTANTIALLY TO SAID OIL FORMATION WITH A WATER LINE EXTENDING DOWN THE OUTER ANNULAR SPACE AND THE TUBING STRING BEING IN OPEN COMMUNICATION WITH THE CASING AT THE LEVEL OF THE OIL FORMATION, THE METHOD OF TREATING SAID OILBEARING FORMATIONS COMPRISING FLOWING STEAM DOWN SAID TUBING STRING, INJECTING SAID STEAM INTO THE OIL FORMATION FOR A TIME AND AT A PRESSURE SUFFICIENT TO REDUCE THE VISCOSITY OF SAID OIL AND FORCE IT TO A PRODUCING WELL IN COMMUNICATION WITH THE SAME OIL FORMATION, REDUCING THE CONVECTION HEAT LOSS FROM SAID TUBING STRING BY CREATING A PARTIAL VACUUM ON SAID INNER ANNULAR SPACE, REDUCING HEAT LOSS FROM SAID TUBING STRING BY CIRCULATING COOLING WATER IN AND OUT OF SAID OUTER ANNULAR SPACE TO PREVENT THERMAL EXPANSION OF SAID CASING.