Three ASP (Alkaline, surfactant and polymer) flooding projects and one multicomponent foam flooding project have been carried out in Daqing Oilfield. The increases of oil recovery rates are all above 20% (OOIP). One of the major troubles that happened during the three ASP flooding projects and the multicomponent foam flooding project was silicate scale deposition in the tubings of production wells which caused frequent downhole operation failure. To prevent scale deposition in production wells, a scale inhibitor, which works well in brines of pH values as high as 12 was developed. The scale inhibitor is effective both on carbonate scale and on the mixed scale of carbonate and silicate. The scale inhibitor was tested on 6 production wells in two ASP flooding project zones. The pull-out period of the tested production wells were elongated from 1 month to 9 month during the test.

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