Research On Annular Corrosion Behavior Of CO₂ Injection Well And Oil-based Annulus Protection Liquid

Greenhouse gas CO₂ emissions from industrial production are the main factors affecting global warming.At present,the main technology of emission reduction is CCUS（Carbon Capture,Utilization and Storage）,and its main application is enhanced oil recovery of CO₂ oil recovery.However,in the process of CO₂ oil recovery it was easy to cause the sealing failure,resulting in a serious corrosion risks of oil line and casing pipe.The risks of corrosion perforation and fracture of pipe column were increased,affected the safe production of gas injection well.Therefore,it was urgent to choose proper annulus protection liquid to restrain corrosion,so as to ensure the integrity of the well.However,this paper studied the corrosion of well injected CO₂ for an oilfield,mainly including the following points:（1）Used static high-temperature and high-pressure（HTHP）autoclave to simulate the working condition of supercritical and non-supercritical CO₂,the steel grades of N80 and P110 were tested and analyzed at different temperatures（30℃,60℃,90℃,120℃ and 150℃）and CO₂ partial pressures（5MPa、8MPa、10MPa、15MPa and20MPa）,and the SEM and EDS were used to analyze the microstructure of corrosion products,obtained the corrosion law of two kinds of steel and analyzed the corrosion characteristics of different working conditions.（2）Based on the results of corrosion evaluation of the P110 and N80 at different temperatures and CO₂ partial pressures,the corrosion behaviors of two kinds of steel in the supercritical and non-supercritical environments were compared and analyzed.The corrosion of carbon steel in supercritical CO₂ phase was worse than that of gaseous CO₂.The corrosion in liquid phase containing supercritical CO₂ was more serious than that in the liquid phase containing gaseous CO₂.（3）Nine kinds of corrosion inhibitors were screened by experiments of mixtures,and the basic oil and corrosion inhibitor preparation for oil-base annulus protection liquid were.preliminary optimized.Using electrochemical experiments optimize the corrosion inhibitors with good compatibility again.Through experiment of weight loss corrosion to test the cooperativity for various active components in oil-based annulus protection fluid,the protection fluid was optimized design,developed a new formula of it.（4）By utilizing HTHP autoclave to simulate the supercritical CO₂ environment of wellbore,the experiment of the protective effect evaluation of the oil-based annulus protection fluid carried out.The results show that the corrosion rate of carbon steel can be controlled at about 0.01 mm/a in this protection fluid,which was much lower than that of oilfield corrosion control index.The results of this paper provided technical support for the annulus protection of CO₂ injection well.