HCO3‾濃度對油氣田中CO2腐蝕的影響

Effect of HCO3－ Concentration on CO2 Corrosion in Oil and Gas Fields

利用動電位掃描和失重法研究了HCO3－濃度對油氣田中CO2腐蝕的影響。高溫高壓腐蝕試驗的研究結果表明，隨著介質中HCO3－濃度的增加，材料的腐蝕速率下降，介質的pH值增大。腐蝕產物膜的SEM、EDS、XRD分析表明，當HCO3－濃度比較低時，腐蝕產物主要為FeCO3晶體，當HCO3－濃度比較高時，腐蝕產物主要為Ca、Mg的化合物，形成Ca（Fe,Mg）（CO3）2複鹽。在高pH值下，Ca2+、Mg2+比Fe2+更容易沉積出來。動電位極化曲線表明，當HCO3－濃度低於0.042 M時，隨著HCO3－濃度的增大，溶液pH升高，H+的還原速率下降，陰極電流密度下降；當HCO3－濃度達到0.126 M時，溶液中的H2CO3、HCO3－的直接還原占主導地位，HCO3－濃度的增大加速陰極過程。對於陽極過程，HCO3－濃度低於0.042 M，主要為活化過程，而且隨HCO3－濃度的增大，陽極溶解的電流密度下降；HCO3－濃度增大到0.126 M時，陽極過程出現明顯的活化－鈍化行為。

The effect of HCO3－ concentration on CO2 corrosion were investigated by polarization measurement of potentiodynamic scans and weight loss method in this paper. Under high pressure and high temperature, the corrosion rate of steel X65 decreased with the increase of HCO3－ concentration while pH increased. SEM, EDS, XRD results of the corrosion scales indicated that a typical FeCO3 crystallite was found at low HCO3－ concentration but Ca(Fe,Mg)(CO3)2 at high HCO3－ concentration. Ca2+, Mg2+ precipitated prior to Fe2+ at high pH value. Potentiodynamic polarization curves showed that the cathodic current density decreased with increase of HCO3－ concentration at low HCO3－ concentration. When HCO3－ concentration reached 0.126 M, increasing HCO3－ concentration promoted cathodic reactions. Anodic behavior was an active process at low HCO3－ concentration and the anodic current density decreased with the increase of HCO3－ concentration. An evident active-passive behavior exhibited in anodic process at 0.126 M HCO3－.