Oil Recovery by Heat From In Situ Combustion

This paper presents a comprehensive and up-to-date review of the mechanics, operating variables and probable economics of the in situ combustion method of oil recovery. It distinguishes between the continuous burning and "heat wave" processes, and points out some of the advantages and disadvantages of each. Although several useful papers have been published on the results of laboratory experiments, information on the results of field tests has been only fragmentary. In order to present a coherent picture of the present status of the in situ combustion method of oil recovery, the author has combined unofficial information on field tests with laboratory data to present some figures-at least some "ball park averages", for petroleum technologists who might be considering a trial of the process. Introduction In situ combustion basically consists of igniting the oil in porous reservoir rock with a suitable ignitor and driving a combustion zone through the reservoir toward producing wells with compressed air, with or without recycle gas. This process differs from other thermal processes in which heat is generated at the surface and injected into the reservoir via hot water, gases, or steam. The in situ principle appeared in 1923 (first U.S. patent) and since 1948 10 field experiments have been conducted in various parts of the U.S., Canada and South America, including one test in Colorado oil shales. Approximately 10 pilot tests are currently being conducted and large commercial operations are planned by several companies. Mechanism During an in situ operation very little reservoir oil is consumed for the combustion front creates hot gases which force oil and water to producing wells. The produced oil is practically unaltered since it is not subjected to cracking temperatures. Actually, during most of the life of the operation, the fluids entering the producing wells are at or near the original reservoir temperature. Fig. 1 shows four coexistent but distinct transient regions which exist between the injection and producing wells.