A Study On CO₂ Corrosion Characteristics Of High Temperature And High Pressure Thermal Recovery Well Strings

During the production process of heavy oil thermal recovery wells injected with multiple thermal fluids,the injected multiple thermal fluids contain CO₂,O₂ and other gases,which will cause serious corrosion to the pipe string.In this paper,for the oil well pipe material N80,a high temperature autoclave is used to perform simulated corrosion tests in a hot fluid environment.The weight loss method is used to obtain the corrosion rate of N80 steel at different temperatures and different hot fluid components,Analyze the effect of corrosion products on the corrosion rate with surface analysis methods?SEM,XRD?.The main conclusions reached are as follows:?1?in a single CO₂ environment,the peak corrosion rate of N80 steel corresponds to a temperature of 100?.As the temperature increases,the corrosion product film gradually becomes denser,and the grains of the corrosion product become finer,thereby protecting the material.Reduce the material's corrosion rate;in a single O₂environment,the corrosion products are loose and easy to fall off,and the porous membrane structure is easy for oxygen and solution ions to penetrate into the matrix,so that the corrosion rate of N80 steel increases with temperature and concentration increase.?2?Under the co-existing environment of CO₂-O₂,when the temperature is higher than 100?,the corrosion rate of N80 steel gradually decreases and increases with the increase of CO₂ content,the presence of oxygen will generate an uncertain intermediate.Products and oxidation products?Fe₂O₃,Fe₃O₄?,thereby destroying the integrity and compactness of the FeCO₃ film produced by the corrosion,so the average corrosion rate of N80 steel is larger and greater than the corrosion rate in a single CO₂ or O₂ environment at the same temperature.?3?After adding inhibitors in different gas environments,the degree of corrosion of N80 steel has weakened,especially in the coexisting environment of O₂ and CO₂-O₂,the corrosion rate of N80 steel decreases significantly,but the average corrosion rate is still relatively large;in the CO₂environment,because the corrosion rate is relatively small without the addition of corrosion inhibitors,the corrosion rate decreases after the addition of the corrosion inhibitor is limited,so the corrosion rate does not reduce significantly.