Study on corrosion law of coiled tubing in high CO2 gas field

The corrosion rates of CT80 grade coiled tubing steel (CT80) and 2205 duplex stainless steel (2205DSS), as well as other attachments, were determined using the weight loss method in a high-temperature and high-pressure autoclave to simulate operational corrosion conditions. The rates were compared with the predicted rates based on BP (backpropagation) neural network optimized by genetic algorithm, in response to the severe corrosion issue encountered during coiled tubing operations in high CO2 gas fields in Sichuan, China. In the gas phase, the results revealed that with the increase of the temperature and the CO2 partial pressure in the high CO2 gas field, the corrosion rate of CT80 gradually increases, while the rate of 2205DSS remains relatively stable and lower than that of CT80. In the liquid phase, the corrosion rate of CT80 exhibits an initial increase followed by a subsequent decrease with increasing temperature and partial pressure, while the 2205DSS corrosion rate remains slightly low and fairly stable. Furthermore, the XRD results of the corrosion product in the liquid phase revealed a higher corrosion rate on CT80 due to its loose and porous film structure, with FeCO3 and Fe2O3 being the main corrosion products. In contrast, 2205DSS exhibited only slight corrosion, characterized by a denser corrosion product film primarily composed of Cr2O3. The average error between the measured values and model calculated values is ∼15%, indicating that 2205DSS exhibited better wear resistance, making it suitable for application in the high CO2 gas field.