Effects of CO2 Solubility on Corrosion of N80 Tubing in Formation Water

This study systematically investigates the influence of CO2 solubility on the corrosion behavior of N80 tubing in simulated formation water under controlled high-temperature and high-pressure conditions. The corrosion behavior was investigated through a methodology combining CO2 solubility quantification obtained from a specialized testing apparatus with pitting rate calculations derived from corrosion tests. The morphology and composition of corrosion products were characterized using scanning electron microscopy, energy-dispersive x-ray spectroscopy, x-ray diffraction, and 3D optical profilometry. Results indicate that CO2 solubility varied nonlinearly with temperature and pressure, increasing with pressure under isothermal conditions but exhibiting a complex nonmonotonic relationship with temperature under constant pressure. A strong correlation was observed between elevated CO2 solubility and accelerated corrosion, with iron carbonate (FeCO3) identified as the primary corrosion product. Microstructural analysis revealed that under high-pressure conditions associated with elevated solubility, the corrosion product film exhibited compromised protective capability, characterized by high porosity and microcracking. This defective film facilitated the development of localized corrosion, which manifested as widely distributed pits of varying depths. A pronounced increase in the maximum pitting rate was observed, highlighting a shift toward localized damage mechanisms.