Experiment And Modeling Of The Seepage Characteristics In Foam Flooding

With the ever-increasing demand of petroleum energy in China and difficulty of exploration, enhancing the developed oil fields oil recovery became more and more important. Foam flooding, as the rapidly developed and novel tertiary oil recovery technique, could effectively enhance oil recovery for its special characteristics. However, the seepage mechanism of foam displacement system in porous media was very complicated and the correct and reasonable understanding and description of seepage characteristics and displacement mechanism was the key problem of reservoir adaptability and oil increment effect. The fundamental study of foam seepage characteristics was of practical importance and theoretical value.The physical simulation study of foam flooding and enhanced foam flooding displacement systems was conducted in both oil-free and oil-bearing models with the aid of advanced foam displacement experiment system of TEMECO company in the United States. The effects of gas/liquid ratio, injection mode, polymer and permeability on foam plugging effect were discussed. Analytical model based on fractional flow theory and mathematical model describing enhanced foam flooding based on molar weight conservation of foam component were established respectively. Formulations with definite physical meanings such as foam generation rate, natural coalescence rate and oil-contacting coalescence rate were developed and numerical simulation was conducted. The multistage matching approach of enhanced foam flooding experiment parameter was first put forwarded, which eliminated or decreased the multiplicity solutions of undetermined parameters as much as possible and achieved the combination of physical simulation and mathematical simulation. Then the distribution of generating rate, natural coalescence rate, oil-contacting coalescence rate and the foam migration characteristics were studied , the partition pattern of foam migration in porous media was described and the seepage characteristics of enhanced foam flooding was systematically analyzed. Foam concentration in gas phase was used to characterize the foam stability and the influencing factors of foam stability were discussed. The relation between displacement effect of enhanced foam flooding and foam stability was analyzed and the displacement mechanism of enhanced foam flooding was brought into cognition, which was conducive to the improvement and development of foam flooding filtration theory and improvement of enhanced foam flooding effect and ultimately enhanced oil recovery.It was indicated that polymer in the enhanced foam flooding system have compound effect by means of decreasing oil coalescence rate, which strengthened foam stability and enhanced considerably oil recovery. The displacement characteristic of foam was characterized as piston-like displacement under the oil-free condition. The foam displacement process could be divided into three parts: growth zone, steady state zone and decay zone under oil-bearing condition. Foam flooding was a dynamic equilibrium process from the aspect of displacement mechanism. The front coalescence foam could be replaced by subsequent stable foam and the foam could still be stable and advance in the process of follow-up water flooding. Profile control mechanism played the main role in foam injection stage, which expanded vertical sweep volume. The enlargement of plane sweep area mechanism dominated in the stage of water cut recovery. The reservoir and injection influencing factors of foam flooding effect were listed in proper order as follows: plug length, oil viscosity, gas/liquid ratio and injection timing. The influencing factors of foam stability were successively gas/liquid ratio, polymer concentration and variation coefficient.