Abstract
In application of Alkali-surfactant-polymer flooding, people always follow after ultra low IFT and negate the effect of ASP solution viscoelasticity on displacement efficiency. For getting the ultra low IFT, ASP solutions need the high concentration of alkali, for example, the ASP flooding needs 1.2%wt NaOH in Daqing oilfield. It brings not only many new technological problems such as scale production in well bore, sticking of pump, reduction of injectivity etc, but also decrease of polymer viscoelasticity. In addition, the selectable range of surfactant for ASP flooding falls a definite limitation due to the restriction of ultra low IFT.
As to ASP flooding in the pilot area of Daqing oilfield, the analysis of ASP solution's rheology and physical simulation experiments have been carried out for studying the effect of alkali on viscoelasticity of displacing phase and the effect of viscoelasticities of ASP solution on displacement efficiency in this paper. Experiments include two types, macrodisplacements and micro-displacements. Cores have artificial heterogeneous models, natural cores and micro-models. The results show that decreasing alkali concentration increases the viscoelasticity of ASP solution, and the displacement efficiencies of ASP solution with low alkali concentration aren't less than that with high alkali concentration and ultra low IFT. At same time, the effect of ASP solution's viscoelasticity on displacement of residual oil in different diameter pores of parallel connection has been analyzed theoretically. The limit of capillary number theory has been discussed in ASP flooding. The mechanism of ASP flooding has been recognized again. The mechanism that viscoelasticity is more important than ultra low IFT as a factor of affecting displacement efficiency has been confirmed. Therefore, Decreasing the amount of alkali and weakening the demand of low IFT not only enlarges the selectable range of surfactant and decreases the costs of ASP flooding, but also solves the problem of alkali scale, and are of great importance to the further development of ASP flooding and its application.
