Effect of HCO3− concentration on CO2 corrosion in oil and gas fields

Abstract The effect of HCO 3 − concentration on CO 2 corrosion was investigated by polarization measurement of potentiodynamic scans and weight-loss method. Under the conditions of high pressure and high temperature, the corrosion rate of steel X65 decreased with the increase of HCO 3 − concentration, while pH of solution increased. SEM, EDS, and XRD results of the corrosion scales indicated that the typical FeCO 3 crystallite was found at low HCO 3 − concentration but Ca(Fe, Mg)(CO 3 ) 2 was found at high HCO 3 − concentration, Ca 2+ and Mg 2+ are precipitated preferential to Fe 2+ at high pH value. Potentiodynamic polarization curves showed that the cathodic current density decreases with the increase of HCO 3 − concentration at low HCO 3 − concentration. When the HCO 3 − concentration reaches 0.126 mol/L, increasing HCO 3 − concentration promotes cathodic reactions. Anodic behavior is an active process at low HCO 3 − concentration and the anodic current density decreases with the increase of HCO 3 − concentration. An evident active-passive behavior is exhibited in anodic process at 0.126 mol/L HCO 3 − .