超级13Cr完井管柱的腐蚀失效原因

Corrosion Failure Causes of Super 13Cr Completion Tubing Strings

通过对某失效超深、超高温高压气井超级13Cr完井管柱的内表面腐蚀检测,结合室内腐蚀试验,分析管内表面状态、酸化缓蚀剂等对完井管柱腐蚀的影响,探讨该气井管柱的腐蚀失效原因。结果表明:超级13Cr完井管柱内壁均匀腐蚀轻微,随井深增大、温度升高,管柱内壁点蚀严重程度增强,在6 000 m左右,最大点蚀深度高达645μm;酸化缓蚀剂与超级13Cr完井管柱不完全匹配,且管柱内壁存在吸附单质铜膜,膜的覆盖不致密会导致较为严重的点蚀;完井管柱内壁氧化皮去除不彻底,且存在表面缺陷,促进了点蚀的萌生及应力腐蚀开裂(SCC)裂纹的形核与发展,严重影响到管柱的结构完整性,最终导致管柱腐蚀失效。

Combining with the corrosion test in laboratory,the influence of inner surface state,acidizing corrosion inhibitor etc.on the corrosion of super 13Cr completion tubing strings was analyzed by inner surface corrosion detection,and the corrosion failure causes for the super deep,super high temperature and high pressure gas well were discussed.The results showed that uniform corrosion was very slight on the inner surface of super 13Cr completion tubing strings,and pitting became more serious with the increase of well depth and temperature,the maximum pitting depth was up to 645 μm at about 6 000 m depth.The acidizing corrosion inhibitor did not display a good matching ability with the super 13Cr completion tubing strings,and there existed metal Cu scale adsorbing on the inner surface,which was not covered densely and thus led to serious pitting of super 13Cr completion tubing strings.The oxide scale on the inner surface of super 13Cr completion tubing strings was not removed completely,and there were some surface defects which promoted the occurrence of pitting and the crack nucleation and expansion of stress corrosion cracking （SSC）.Therefore,it affected severely the structural integrity of completion tubing strings and resulted in the corrosion failure eventually.