Study On Numerical Simulation Of Foam Flooding In Low Permeability Reservoir

Low permeability reservoirs are widely distributed in China, and these kinds of reservoirs generally have the characteristics of low porosity, low permeability and low recovery. Conventional oil recovery method, such as water injection and gas injection, can improve the development effect for low permeability reservoirs. However, in mid-late development stage it has low sweep efficiency of injected fluid, resulting from not being injected and water or gas breakthrough, which makes low permeability reservoirs have low production and low recovery. Foam flooding can enhance oil recovery of low permeability reservoirs, because this recovery method can improve the mobility ratio, increase the displacement efficiency by reducing the interfacial tension of oil-water, increase the formation energy, as well as reduce the threshold pressure and injection pressure. So it is important to carry out the numerical simulation of foam flooding in low permeability reservoirs, which has directive significance to develop low permeability reservoirs effectively and economically.In this paper low permeability reservoirs are studied as the research objects, and enhancing the low permeability reservoirs recovery as the goal, the advantages and the disadvantages of common enhancing oil recovery methods for low permeability reservoirs are analyzed and compared. Foam flooding is a better way to enhance oil recovery for low permeability reservoirs. On the basis of the study of the complex seepage characteristics of foam flooding system and its displacement mechanism, the mathematical model of N2foam flooding was established, and the implementations of foam flooding in UTCHEM, Eclipse and CMG were analyzed and compared. Finally, numerical simulation of foam flooding for low permeability reservoirs was studied in this paper. By using Orthogonal Experimental Design, the influences of injection mode, slug size, surfactant concentration and gas-liquid ratio on oil recovery were analyzed.Based on the research above, main results were obtained as follows:(1) According to development characteristics of low permeability reservoirs, the merits and demerits of different kinds of enhancing oil recovery methods were analyzed for improving the development effects in low permeability reservoirs. Foam flooding is one better way to improve the development effects of low permeability reservoirs, which can increase sweeping efficiency and oil displacement efficiency.(2) Mechanisms of foam formation and destruction were analyzed and studied, and the effects of the molecule structure of surfactant, wettability, temperature, the existence of oil and interfacial tension on foam stability were also studied.(3) On the basis of studies of seepage characteristics and foam displacement mechanism, the mathematical model of N2foam flooding was established, and the effects of foam on the relative permeability of formation fluids were also analyzed, and the implementations of foam flooding in UTCHEM, Eclipse and CMG were analyzed and compared.(4) Mechanical research of numerical simulation in one-dimensional core was studied, which quantificationally proved foam flooding is better than water flooding in low permeability oil reservoirs. Meanwhile, the effects of foaming agent concentration on the foam displacement efficiency were analyzed. The higher foaming agent concentration is, and the higher foam displacement efficiency is. However, there exists an optimal foaming agent concentration.(5) Finally, the orthogonal experiment design was adopted, and9cases were designed in L9(34) orthogonal table, so foam flooding to enhance oil recovery was studied in one low permeability reservoirs. In this research the effects of injection mode, slug size, surfactant concentration and gas-liquid ratio on the oil recovery were analyzed, and the optimal development program of foam flooding was optimized. Comparing with water flooding program, the optimed foam flooding could enchance oil recovery by7.32%.