Unraveling the Impact of Cr Content on the Corrosion of Tubing Steel in High CO₂ and Low H₂S Environments

A theoretical foundation for selecting corrosion-resistant materials is necessary to address the corrosion risks in complex oil and gas fields and tubing for CO₂ capture, utilization, and storage (CCUS). To achieve this, experiments were conducted using actual oilfield simulated formation water as the corrosive medium. Weight-loss corrosion tests and surface analysis methods were employed to investigate and compare the corrosion of four steel materials (C110, 3Cr, 5Cr, and 9Cr) in high mineralization, CO₂, and trace H₂S coexistence environments. The results show that all materials experience CO₂-dominated corrosion under CO₂ and trace H₂S conditions, with corrosion rates exceeding the controlled limit for oilfields (0.076 mm/y). The corrosion severity is classified as extremely severe, and the corrosion products mainly comprise a mixed carbonate of FeCO₃ and CaCO₃. Both uniform and localized corrosion rates decrease gradually with increasing chromium content in the materials. The experimental study demonstrates that chromium has good corrosion resistance. The morphology of the corrosion product film transitions from irregular particles to rhombohedral blocks or flakes with increased chromium content. Carbon steel primarily forms Fe_xCa_1-xCO₃ corrosion products with a small amount of Fe₂O₃ inclusion, while corrosion products in chromium-containing steel include Cr₂O₃, Cr(OH)₃, Fe_xCa_1-xCO₃, and Fe₂O₃. As the chromium content in the steel material increases, the content of Ca and Cl elements in the corrosion product film gradually decreases. These findings provide valuable insights into the corrosion behavior of different steel materials under the challenging conditions of high mineralization, CO₂-rich, and trace H₂S environments. They contribute to the theoretical basis for selecting suitable corrosion-resistant tubing materials for oil and gas operations, including CCUS, enabling the industry to mitigate corrosion risks effectively.