拉应力条件下油气井套管腐蚀机理研究

结合断裂力学理论，通过慢应变拉伸等系列实验，探讨了拉应力加速油气井套管腐蚀的机理，认为腐蚀和碰伤会加快套管裂纹的孕育，断裂韧性和断裂强度因子的变化对裂纹的扩展起加速作用。慢应变拉伸实验结果表明，拉应力作用下，钢材在强腐蚀性地层水中的力学性能比空气中明显下降，而添加缓蚀剂后，力学性能得到改善；断口电镜扫描显示在地层水中断口的裂纹增多，同时断裂敏感参数也说明钢材在地层水中出现了应力腐蚀断裂特征；试样失重实验结果证明应力腐蚀速率比无拉应力时高出13.6％～24％，添加缓蚀剂可使应力腐蚀速率显著降低；能谱分析表明缓蚀剂通过迅速成膜减缓腐蚀对裂纹的扩展作用，较大幅度减缓了钢材的应力腐蚀速率，同时可以使钢材的力学性能的受损幅度降低。

CORROSION MECHANISM OF CASING UNDER TENSILE STRESS IN OIL/GAS WELL

The mechanism that corrosion rate of casing in oil or gas well is accelerated by tensile stress was studied by series experiments combined with fracture mechanics theory. Process of fracture origination will be shortened by corrosion and dog marks,and fracture extension will be accelerated due to change of fracture toughness and intensity factor. Experimental results show that stress corrosion cracking characteristics occurred on fractured steel samples with tensile stress which were put inside strong corrosive formation water,and corrosion rate is about 13.6%-24% more than the rate of the other samples without tensile stress. Corrosion inhibitor can quickly form a film to shield from steel and decelerate fracture speed,and reduce the corrosion rate of steel sample and reduce the weakening extent of steel sample.