塔河油田注气井井筒氧腐蚀机理研究

Study of Oxygen Corrosion Mechanism in Wellbore Tube for Gas Injection in Tahe Oilfield

塔河油田缝洞型油藏采用氮气驱可有效提高剩余油的采出程度,但注入的氮气中含2%~5%的氧气,使得井筒腐蚀严重。采用失重法、EIS极化曲线法和电化学阻抗法研究了塔河油田在注氮气提高采收率条件下的氧腐蚀特点,得到了腐蚀速率、腐蚀阻抗谱和腐蚀动力学曲线。研究表明,腐蚀速率随着温度和压力的增加而增加,腐蚀速率在井深2 500 m处达到了0.446 mm/a;注气柱塞泵下入井深1 818 m时,泵经过117 h工作后已经被腐蚀产物全充满,这与现场的检泵周期基本吻合。据此建议塔河油田注气抽油泵下入深度应不超过2 500 m;注气井筒在焖井过程中应加入除氧剂,并可以考虑用稀油代替水作为顶替液。

Due to 2% ~ 5% oxygen content in injection nitrogen gas for EOR of fracture-cavity type reservoir in Tahe Oil- field, wellbore tube suffers heavy corrosion. Weight-loss method, EIS polarization curve method and electrochemical impedance method are applied in studying the oxygen corrosion characteristics. And the corrosion rate curves, corrosion resistance spectrum and corrosion dynamic curve are obtained. The research results show that the corrosion rate increases with the increment of temperature and pressure, and reaches 0.446 mm/a in the wellbore depth of 2 500 m; After work- ing for 117 h in the wellbore depth of 1 818 m, the piston pump is fully filled with corrosion products, which is basically in coincidence with the pump inspection period. It is suggested that the working depth of the piston pump used in Tahe Oilfield should not be more than 2 500 m; Deoxidizer should be added into the gas injection wellbore during soaking process, and thin oil can be considered to replace water as displacement liquid.