Study on corrosion laws of casing steels in CCUS injection wells in simulated cement pore fluids

Casing corrosion often occurs in CCUS injection wells and affects its safe service life. In a HTHP kettle, corrosion experiments on the inner and outer walls of N80 and L80-13Cr casing were carried out under different CO₂ partial pressures in order to reveal the microscopic corrosion mechanism with characterization methods. Based on the weight-loss corrosion rate, local corrosion rate, collapse resistance strength, residual tensile strength, internal compressive strength and cost of casings, a hierarchical material selection model was established to evaluate the suitability of N80 and L80-13Cr steels and the results for the rational selection of materials. The corrosion rate of casings increased with the increase in CO₂ partial pressure. In a simulated pore environment, CaCO₃ and SiO₂ formed a passivation film to alleviate uniform corrosion. In addition, loose CaCO₃ scale caused the uneven product film, thus intensifying local corrosion. Cr element in L80-13Cr steel repaired the product film and reduced the corrosion rate, thus showing the stronger pitting corrosion sensitivity. It was recommended that N80 steel could meet the corrosion resistance requirements of oil casings in CCUS injection wells.