Corrosion Behavior and Anti-Corrosion Strategies for Pipelines in CO2-Enhanced Oil Recovery Projects

CO2-enhanced oil recovery (CO2-EOR) leads to a progressive increase in the CO2 content of produced fluid, exposing pipelines to a harsh acidic corrosive environment. In the present study, the typical CO2-EOR process flow was classified, and the corrosion behavior of 20# steel and 316L stainless steel was simulated under operating conditions involving different CO2 partial pressures (0.5 and 1 MPa) and temperatures (25 and 45 °C). The inhibition performance of an imidazoline corrosion inhibitor and a tung oil-rosin-modified imidazoline corrosion inhibitor under CO2-EOR operating conditions was compared, and commonly used corrosion monitoring methods were also evaluated. The results showed that, with increasing CO2 partial pressure and temperature, the corrosion rate of 20# steel increased continuously, the corrosion products became denser, and localized pitting corrosion occurred, indicating a transition from moderate to severe corrosion. Although the corrosion rate of 316L stainless steel also increased continuously, its growth rate remained relatively low, and the material consistently remained within the mild-corrosion range. After the addition of a conventional imidazoline corrosion inhibitor, the corrosion rate decreased to 0.0832 mm/a, with an inhibition efficiency of 69%. By contrast, application of the tung oil-rosin modified imidazoline corrosion inhibitor reduced the corrosion rate to 0.0301 mm/a, and the inhibition efficiency reached 89%. Considering safety and economic factors comprehensively, pipeline materials were optimally selected as follows: 20# steel was selected for gathering pipelines extending from the Christmas tree to the oil–gas separator at the station, supported by corrosion inhibitor injection and a corrosion-monitoring system; 316L stainless steel was adopted for pipelines between the oil–gas separator and the dehydration equipment; 20# steel was used for pipelines between the oil–gas separator and the oil–water treatment station; and 20# steel was selected for the system after natural gas dehydration, while low-temperature-resistant steel should be considered when the temperature is below −20 °C. Corrosion monitoring should preferably involve combined methods: the coupon method for straight pipe sections and the ultrasonic fixed-point thickness measurement method for elbow sections.