Study on Basic Properties of Alkali‒Surfactant‒Polymer Flooding Water and Influence of Oil-Displacing Agent on Oil–Water Settlement

The basic properties of alkali–surfactant–polymer (ASP) flooding produced water and effect of oil displacing agent on the stability of flooding produced water were obtained by measuring and analyzing the water quality of Zhong-106, etc., flooding water from Daqing Oilfield and the relationship between oil content-settling time and oil displacing agent-oil drop size. The addition of ternary oil displacement agent to ASP flooding water greatly increases the difficulty of oil–water separation, higher concentration, and worse separation effect after standing. Surfactant alkali and polymer have effect of promoting the reduction of oil droplet size distribution and are all affected by the initial oil content and pH. When pH is between 10.5 and 11.75, the average particle size of oil drop in ASP produced water changes the most significantly, and as the alkali content increases, the pH of the produced water rises faster. Alkali reacts with the active substances contained in the crude oil in the produced water, such as organic acids, thereby increasing the pH of the produced water. The pH of the produced water changes smoothly when alkali content is 5000 mg/L, but all are less than alkaline flooding water, which shows that alkali can promote the partial hydrolysis of polymer in the produced water and the process can reach equilibrium. The ASP flooding produced water after 48 h of settling formed a trace amount of nano-oil droplets, also accompanied by the accumulation and separation of a part of the oil droplets.