Corrosion Rate and Service Life Prediction of CO₂ Injection Well String

With the continuous application of CCUS technology in oil fields, the phenomenon of CO₂corrosion of downhole string has attracted great attention, and it is urgent to apply the corrosion rate model considering the influence of corrosion rate change with time under high CO₂partial pressure environment. By simulating the corrosion of Q125, 3Cr and13Cr pipes under the temperature of 80 ℃-120 ℃ and CO₂partial pressure of 15 MPa-30 MPa, the three corrosion rate prediction models considering the influence of temperature, CO₂partial pressure and corrosion time were established, and the safe service life of Q125 casing was predicted. The results show that under the same CO₂partial pressure, the corrosion rates of Q125 and 3Cr pipes increase first and then decrease with the increase of temperature, and the corrosion rate of 13Cr pipe increases with the increase of temperature. The corrosion rates of the three pipes increase with the increase of CO₂partial pressure. The uniform and variable speed corrosion rate models of Q125 pipe are applicable, and the variable speed corrosion model is suitable for 3Cr and 13Cr pipes. The tensile safe service life of Q125 casing gradually decreases with the increase of CO₂partial pressure, and the shortest tensile safe service life is about 12 years.