Immiscible Multi-Phase Fluid Displacement in a COFCAW Process
Authors: Popa Constantin G. 
Published: December 2007

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.
This paper was prepared for the Improved Oil Recovery Symposium of the Society of Petroleum Engineers of AIME, to be held in Tulsa, Okla., March 22–24, 1976. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made. provided agreement to give proper credit is made. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and with the paper, may be considered for publication in one of the two SPE magazines.

Abstract
The paper presents a method to describe more accurately the displacement of two or more immiscible fluids by one or more immiscible fluids. The method was applied in a COFCAW process to describe the saturation distribution in a multiphase immiscible displacement which occurs ahead of the comb in a linear reservoir. Graphical results are shown which facilitate the evaluation of displacement efficiency. The method can be used to determine the optimum water-air ratio to be injected for improving displacement in this process. One example calculation is provided to demonstrate the use of this method.

Introduction
The Combination OF Forward Combustion And Waterflooding (COFCAW) has been proved to be a practical and efficient method for tertiary oil practical and efficient method for tertiary oil recovery. By injecting an air-water mixture instead of air only into an underground combustion process, the losses of heat are minimized by the process, the losses of heat are minimized by the vaporization of injected water at the fire front. Although the formed steam and gas will travel faster than the combustion front, the steam will condense and improve the oil recovery. Laboratory experiments have shown the temperature profile falls abruptly ahead of the combustion front to the initial reservoir temperature. The process appears to be very complex and the bank concept has been developed. By this concept there is accepted existence of a multiphase fluid displacement ahead of the combustion front. The gas resulting from combustion together with the water resulting from condensed steam will displace the fluids existing ahead of the combustion front.
The purpose of this paper is to describe more accurately the saturation profile appearing ahead of the combustion front in this process. The process is described similar to that of two immiscible fluids (gas and water) being injected simultaneously to displace the fluids initially existing in the porous medium. By knowing the saturation profiles it is possible to evaluate the efficiency of displacement possible to evaluate the efficiency of displacement for a given gas-water ratio at the inlet face. A multiphase fluid flow theory is presented and the difficulties in applying the method of characteristics are discussed. Further assumptions are made and a simplified method is applied in a linear COFCAW process. The fluids are considered immiscible and process. The fluids are considered immiscible and slightly compressible. The gravity and capillary pressure are neglected. No heat transfer was taken pressure are neglected. No heat transfer was taken into consideration. The theory was applied for two cases, respectively for an unflooded reservoir and a waterflooded reservoir.