Water-alternating-gas injection of CO2 flooding has received attention as a proven gas channeling controlling method for enhancing oil recovery. However, the application of this method led to the coexistence of corrosion and scaling, affecting well productivity. Current single agent has slight anti-corrosion effect, which mainly concentrates on scale prevention. Meanwhile, the treatment means of agent compounding has poor compatibility. Therefore, developing a single agent with both anti-scale and anti-corrosion properties is beneficial to production. In this study, the dehydrated product of cyclization of amine and acid were condensed with aldehydes and ketones under acidic conditions to prepare mannich base imidazoline groups, that could play the corrosion inhibition effect. The imidazoline – phosphate copolymer was synthesized by introducing the scale inhibition of phosphate esters into imidazoline, followed by a grafting reaction. Corrosion and scale inhibition properties of the synthesized agent were evaluated by rotary hanging weight loss method, and the biodegradable performance was analyzed. The results of infrared spectrum characterization illustrated the successful binding between the effective functional groups of imidazoline groups and phosphate groups. The scale inhibition rate of 30 mg/L of the synthesized agent to calcium carbonate (CaCO3) was 92.41%. The corrosion rate of CO2 on steel was 0.061 mm/a when the synthesized agent was added, indicating that the corrosion resistance of the imidazoline – phosphate copolymer was superior than that of most of the reported single agent used for corrosion inhibition and scale inhibition. The chemical oxygen demand of the synthesized agent decreased significantly when aging in the soil where plants grew, and the biodegradation rate of the synthesized agent at 28 days was 70.93%. The single agent of imidazoline – phosphate copolymer exhibited superior performance in solving the problems of corrosion and scaling in the wellbore, which could facilitate the application of captured and buried CO2 in oil displacement, so that meeting the requirements of environmental protection and efficient reservoir development.
Keywords water-alternating-gas injection, carbon dioxide, scale removers, scale remover, imidazoline - phosphate copolymer