Research And Performance Evaluation Of Low Interfacial Tension Foam Flooding System

In this paper, the research literature at home and abroad about foam flooding theory was investigated. The feasibility of the low interfacial tension foam flooding further enlarge swept volume and improve displacement efficiency after polymer flooding was analyzed, methods and indicators to evaluate the foam performance was introduced and compared; the main influencing factors on foam properties were summarized, including molecular structure and concentration of the foaming agent, role of foam stabilizer, formation water medium, temperature and pressure, etc.The indoor experiments of the low interfacial tension foam flooding formula were carried out under Shuanghe oilfield reservoir conditions. Studies on oil-water interfacial tension and foaming properties of different molecular structure surfactant and its complex system of were screened and evaluated. The compound foaming agent system CAB+CDEA was better foaming performance and the low interfacial tension. A variety of foam stabilizing agent compound with foam agent was screened and evaluated, and finally got the best foam composite system. The oil-water interfacial tension and aging stability of foam composite system were determined. The temperature, pH, salinity and total concentration of calcium and magnesium ions influence on foam performance and the oil-water interfacial tension of foam composite system were investigated. The apparent viscosity and voscoelastic were determined use of the Anton Paar rheometer. The experimental results show as follows.①For low salinity characteristics of Shuanghe oilfield reservoir injected water, the anionic-nonionic surfactant AES, the cationic surfactant DTAB and the zwitterionic surfactant BS-12which is the hydrophilic groups of low hydrophilic can reduce the oil-water interfacial tension to approaching10-2mN/m. Under the same hydrophilic group condition, the surfactants which have a moderately hydrophobic carbon chain length (R≈C12-15) or hydrophobic groups containing a benzene ring or a class of benzene ring can reduce interfacial tension to low.②The foaming performance of the anionic surfactant SDS, SLS, anionic-nonionic surfactant AES, and the zwitterionic surfactant BS-12which have different hydrophilic groups are relatively good. The foaming volumes of the surfactants which have the same hydrophilic groups are increasing first and then decreases with the carbon chain length increases. When the hydrophobic carbon chain increases modest, the foaming volume reaches the largest. Such as, the foaming volumes of the zwitterionic surfactant CAB and BS-14reach the largest in which carbon chain length of12-14.③The problem of the confrontation between foaming properties and its ability to reduce the interfacial tension was solved by a large number of surfactant compound experiments. The mixtures of zwitterionic surfactant CAB, BS-14and nonionic surfactant CDEA have obvious synergies in different complex ratio (5:1to1:2), which can reduce the interfacial tension to10-2mN/m and below. But BS-14+CDEA compound has non-foaming, only CAB+CDEA compound has a low interfacial tension and good foaming properties.④Compared the two methods of Ross-Miles and Waring-Blender which to evaluate foam stability of foam agent, the Waring-Blender mixing method has advantages. The formation bubbles of the foam system more dispersed and blistering volume. It can use to evaluate foaming stability of foam agent which has a certain viscosity.⑤The non-viscous foam stabilizer has a negative effect on foam stability of low interfacial tension CAB+CDEA foam system, but the viscous foam stabilizer gain a sticky has a stabilizing effect on foam system. The composite index of PA and CAB+CDEA (5:1) complex foam system is greater than1000mL.min, to meet the requirements of strong foam system. The concentration of PA stabilizer and aging time is less influence on the oil-water interfacial tension of composite foam system. The experiments research on the mechanism of foam stability were carried out, the results show that the stabilized foam system should have a higher surface viscosity to form a stable surface film and have a moderate viscosity of the solution to reduce foam liquid film draining speed.⑥The formula of foam flooding system was determined as follow,3500mg/L (CAB+CDEA (5:1)) foaming agent and1500mg/L PA foam stabilizer. With temperature (50～80℃) increased, the foam volume of foam system increased, the foam half-life to reduce, the foam composite index increased and then decreased; With pH (7～10) increased, foam composite index declined; the salinity (5000-10000mg/L) and calcium and magnesium ion content (50-100mg/L) were less affected on the foam composite index. The increasing of temperature, pH, and salinity can improve the ability of reducing the oil-water interfacial tension of the foam flooding system. The increase in calcium and magnesium ion content was disadvantageous to reduce the oil-water interfacial tension. ⑦The foam fluid of foam system is non-Newtonian fluid within1～100s-1shear rate, in line with the characteristics of the pseudo plastic fluid. The apparent viscosity of foam fluid decreases as shear rate increasing, it shows shear thinning behavior. The foam system has good viscoelasticity in the higher frequency range (1～39Hz), its visco-elastic modulus higher than1Pa. Compared with other polymer viscoelastic, foam system has a very good viscoelasticity.