Effect of HCO_3~- concentration on CO_2 corrosion in oil and gas fields

摘要

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~-.