Study on stability of produced water in ASP flooding based on critical micellar theory

The basic properties of produced water and the effect of oil displacement agent for its stability were obtained, through measuring and analyzing water quality characteristics, relationship between critical micelle concentration-oil displacement agent, temperature, pH and content of inorganic salt, particle size distribution and morphology of Nan4-8 and Sanyuan-6 alkali-surfactant-polymer (ASP) produced water of Daqing Oilfield. The critical micelle concentration of ASP flooding was less than its own concentration, and the double bilayer was formed in system. Critical micelle concentration of ASP produced water was less affected by the system temperature and greatly affected by pH. Polymer increases viscosity of produced water and has the properties of surfactant, which partially hydrolyzes under the action of alkali to form polyelectrolyte and promotes the formation of double electric layer. Therefore, the coalescence of oil droplets in ASP produced water is difficult, and the stability is greatly enhanced. ASP produced water contains a large amount of inorganic salts, which can shield the electrostatic repulsion between the surfactant ion head groups, compresses the thickness of the double electric layer, and promotes the formation of surfactant micelles. When it settles after a certain period of time, part of ASP produced water has a particle size distribution less than 100 nm, the micelles are generated in the system, which enhances the stability of ASP produced water.