Study Of Oil Displacement Effect Factors Of Alkaline/Surfactant/Polymer Flooding System

Alkaline/surfactant/polymer(ASP) flooding system is a lately developed oil displacement technique, but it is a mature technique of tertiary oil recovery. Its displacement mechanism: it uses synergistic effect of alkaline, surfactant and polymer in ASP flooding system to displace oil. Namely, alkaline, the price is cheap, can react with acid component of the oil to bear natural surfactant, which can reduce the loss of artificial surfactant and help surfactant to make oil/water interfacial tension to attain the super-low value; surfactant can lower oil/water interfacial tension, change rock wettability and enhance oil displacement ability; polymer can obviously lower displacing fluid mobility and enhance sweep efficiency. Field practices in Daqing oilfield express that ASP flood can enhance recovery efficiency 20% or so than water flood.The method displays an inspiring application prospects and is widely valued by people. However the cost of ASP flood for oil displacement is higher, and how to further lower its cost and increase the benefit is also the key point that the technique can large-scale applied or not. Through the study of oil displacement effect factor of ASP flood, it tries hard for beneficial work on further lowering the cost and enhancing recovery efficiency in the article. Through systematic indoors physical analogy experiments, it analyzes main effect factors of ASP flood in detail and investigates the increment of viscosity ratio, main slug injection manner and rate, interfacial tension, formation variation coefficient and main slug residual resistance factor to affect the oil displacement effect of the system. It reveals main factors that ASP flood enhances recovery efficiency, namely interfacial tension between ASP flooding solutions and oil, viscosity ratio between ASP flood and oil, injection manner, formation variation coefficient. Aim at the seriously heterogeneous formations, it uses ASP to adjust profile, which can save the dosage of the polymer and provide the basis for succeeding in applying the technique in the field. Through study, conclusions can be drawn as follows: only viscosity ratio between ASP system and oil is kept above 2:1, oil displacement efficiency of ASP flood is able to attain more than 20%; it should adopt super-high molecular weight polymer to replace middle molecular weight polymer at big limit in ASP system, which is the effective path to save the dosage of the polymer; oil displacement efficiency of high concentration and small slug is higher than low concentration and big slug's, and displacement effect of high molecular weight polymer is obviously different with low molecular weight polymer; whether natural core or artificial core, only when balanced interfacial tension of compound system attains 10~3mN/m, the magnitude that the system enhances recovery efficiency is over than 20%, which satisfies the system of requests of enhanced recovery efficiency; formation heterogeneity has an effect on oil displacement efficiency of ASP system, when variation coefficient is 0.7, oil displacement recovery efficiency of ASP system appears biggest value; indepth profile control in the process of ASP flood can save the dosage of the polymer, further increase percolation flow resistance of the displacement fluid, expand swept volume of the displacement fluid and enhance oil recovery efficiency. Experiment research expressess that it can significantly enhance oil recovery efficiency to perform "Sandwich" profile control among main slugs of ASP flood.