Corrosion behavior of carbon steel in formate-based completion fluids saturated with supercritical CO2

Purpose This study aims to investigate the corrosion behavior and mechanism of P110SS steel in supercritical CO2-saturated formate salt completion fluids under high-temperature-high-pressure conditions. Design/methodology/approach Corrosion tests were conducted using weight loss measurements, scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy and electrochemical analysis. The tests were performed under CO2-saturated formate salt solutions at 10 MPa, varying temperatures and formate salt concentrations. Findings The corrosion rate increases with temperature, peaking between 90°C and 150°C (23 mm/a). Corrosion is exacerbated by higher fluid densities and elevated temperatures. The pH buffer significantly reduces the corrosion rate by up to 90% at high temperatures. FeCO3 is identified as the primary corrosion product, with its structure evolving from cracked to flocculent and needle-like, and becoming denser at higher temperatures. The corrosion mechanism is attributed to the formation of a loose, porous corrosion film and intergranular voids, which are responsible for the increased corrosion rate. Originality/value This research provides novel insights into the corrosion mechanism of P110SS steel in supercritical CO2-saturated formate salt fluids, particularly under high-temperature conditions. It contributes to offering practical recommendations for corrosion prevention and material selection in oilfield operations.