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This paper was prepared for presentation at the 1998 SPE International Conference on Horizontal Well Technology held in Calgary, Alberta, Canada, 1-4 November 1998.

Using horizontal wells in a waterflooding process, a higher sweep efficiency for less cost is expected as opposed to the use of classical patterns by vertical wells. However, the use of horizontal wells is very sensitive to the well pattern designed to operate such a process. The paper presents an analysis of how the overall efficiency of a waterflooding process is influenced by the well pattern using horizontal injectors and producers in different configurations. Recent investigations used vertical injectors and horizontal producers, with the horizontal well completed at the top of formation and having its toe close to the injection well, which was perforated at the lower part of formation. This process, known as a short-distance Toe-To-Heel Waterflooding "(TTHW) process", was found sound for the light-heavy oils with viscosity up to 2,000 cP, and proved to have maximum efficiency for relatively thick formations. The general necessity to inject higher water rates, simultaneously with the preservation of a certain control on the injection, prompted the investigation of the use of horizontal wells as injectors both for light-heavy oil and light oil recovery in thin oil reservoirs in a long distance displacement configuration, as well. A two phase two dimensional numerical simulator for thin formations to investigate the Waterflooding by Horizontal Injectors and Producers, including an "areal" TTHW process, was used. Both the sink/source and the discretized well were considered, in order to estimate the effect of pressure drop along both injectors and producers on the oil recovery performance. The results showed that the pressure loss along the horizontal section has a significant influence on the sweep efficiency. A numerical simulation study for 10 oils having viscosities between 1 cP and 150 cP was undertaken. The study was performed for both long-distance and short-distance displacement configurations, although for some oil viscosity values it was made just for illustrative purposes. The main parameters, such as time of water break-through, oil recovery at break-through, sweep efficiency, injection-production pressure drop, etc were analyzed in all cases. For optimization purposes two types of configuration were investigated: a staggered parallel horizontal wells configuration, having their heels in opposite directions and their toes arranged in a direct line, and an L shaped configuration, with perpendicular horizontal wells having their toes relatively close to each other. Introduction The waterflooding efficiency is highly influenced by the pressure loss along the horizontal well section and the geometry of the well pattern. Thus, the pressure loss along the horizontal section of a well will result in a non uniform distribution of the fluid flux along this section1,2. Accordingly, the flow rate is greater toward the heal section of the well and lower toward the toe section of the well, both for a production and an injection horizontal well. As concluded in a previous paper3 it is strongly recommended to use an inverse pattern for an waterflooding process rather than a direct one. As it was shown, due to the preferable tendency of the water to flow from the heel of the injector toward the heel of the producer, for the first case the sweep efficiency is much greater than for the later one.

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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.