镍基合金825在模拟油气井含CO2环境中的耐蚀性研究

针对深层油气井开采过程中的CO2腐蚀问题,采用高温高压釜模拟腐蚀试验和动电位极化曲线、电化学阻抗谱(EIS)等测试手段研究了镍基合金825在苛刻CO2环境中的腐蚀行为。试验结果表明:镍基合金825在210℃、CO2分压4.4 MPa的腐蚀环境中,腐蚀速率为0.015 7 mm/a,均匀腐蚀很轻微,表现出良好的抗均匀腐蚀性能;镍基合金825的阳极极化曲线呈现出明显的钝化区,且在120℃、CO2分压为3.5 MPa条件下存在二次钝化现象;随着温度升高,CO2分压增大,自腐蚀电位负移,腐蚀驱动力变大;EIS表明电化学阻抗谱有明显的容抗弧特征,电荷转移电阻呈减小的趋势,而钝化膜电容呈减少趋势,电化学腐蚀动力学阻滞性能减弱,降低了镍基合金825在模拟工况中的耐蚀性。

Corrosion Resistance of Nickel-Based Alloy 825 in Simulated Oil and Gas Wells Containing CO2

Aiming at the CO2 corrosion problem in deep oil and gas well exploitation,the high temperature and high pressure autoclave simulated corrosion tests,potentiodynamic polarization curve tests and electrochemical impedance spectroscopy( EIS) tests were used to study the corrosion behavior of nickel-based alloy 825 in harsh CO2 environment. Results showed that the nickel-based alloy 825 had a corrosion rate of0.015 7 mm/a in a corrosive environment with a partial pressure of 4.4 MPa at 210 ℃ . The uniform corrosion was very mild,which presented good resistance to uniform corrosion. Meanwhile,the anode polarization curve of nickel-based alloy 825 showed a distinct passivation zone,and a secondary passivation phenomenon was observed at 120 ℃ with CO2 pressure of 3. 5 MPa. As the temperature increased,the CO2 partial pressure increased,and the self-corrosion potential negatively shifted,as well as the corrosion driving force became larger. In addition,EIS indicated electrochemical impedance spectroscopy had obvious capacitance arc characteristics. Charge transfer resistance decreased,and passivation film capacitance declined,which weakened the electrochemical corrosion kinetic retardation and reduced the corrosion resistance of nickel-based alloy 825 in simulation conditions.