In Alkali-surfactant-polymer flooding, although the high concentration of alkali, for example 1.2%wtNaOH in ASP flooding in Daqing oilfield, can lead to an ultra low interfacial tension, it brings many new technological problems such as scale production in well bore, reduction of injectivity resulted from producing of alkali scale etc. The sharply shortened period of checking pump have adversely influenced the production of wells.
In this paper, the effect of alkali on viscoelasticity of displacing phase and the effect of viscoelasticities of ASP solution on displacement efficiency has been studied by studying rheology of ASP solution and physical simulating of ASP flooding which included the macro-displacement experiments in heterogeneous models and micro-displacement experiments to ASP flooding in Daqing oilfield. The mechanism that the viscoelasticity is more important than ultra low interfacial tension as a factor of affecting displacement efficiency has been confirmed. The sorts of surfactant, which can reach ultra low interfacial tension, are limited and expensive. These surfactants solution also need to add a high concentration of alkali to get ultra low interfacial tension. But for adding alkali, the viscoelasticity of ASP solution is decreased, and new technological problems have been brought about. On the contrary, decreasing the amount of alkali and weakening the demand of low interfacial tension can increase viscoelascity of ASP solution. The experimental results show that the displacement efficiencies of ASP solution with low alkali concentration aren't less than that with high alkali concentration and ultra low interfacial tension. The results 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.
In China, It is the first time to study the effects of ASP solution viscoelasticity on displacement efficiency by macro and micro physical simulation. Ultra low interfacial tension is not a necessary condition for enhancing oil recovery. The limit of capillary number theory has been discussed in ASP flooding. The mechanism of ASP flooding has been recognized again.
In 1927, L.C.Uren and E.H. Fahry pointed out that the displacement efficiency was inverse proportion to interfacial tension in water flooding. But it was not paid adequately attention for limit of experiment conditions. In 1966, O.R.Wagner etc have verified the theory that the displacement efficiency can be enhanced when interfacial tension is less than 0.07mN/m. And lower the interfacial is decreased; more high the displacement efficiency can be enhanced. In 1973, the relationship of the capillary number (µ?/s) and oil recovery have been studied by W.R. Foster. The residual oil saturation could be near zero when the capillary number was 10-2 magnitude. To get the value of the capillary number, the interfacial tension must be decreased to 0.001mN/m. R.L. Reed etc have verified the low interfacial tension is important factor to decide displacement efficiency too. When the interfacial tension between oil and water was deceased to 10-1mN/m, the displacement efficiency was enhanced obviously. When it was decreased to 10-3mN/m, the residual oil saturation was close to zero. In Recent twenty years, ultra low interfacial tension has been influencing the study of surfactant flooding technology.