海上注聚井渗氮油管腐蚀失效原因

Reasons for Nitriding Tubing Corrosion Failure of an Offshore Polymer Injection Well

渤海S油田A2井渗氮防腐油管在注聚过程中发现多处腐蚀穿孔,为避免换管柱后再次发生腐蚀失效,通过腐蚀形貌观察、腐蚀产物分析、腐蚀介质分析对A2井油管腐蚀失效原因进行了研究。认为A2井油管部分渗氮层脱落,形成了电化学腐蚀的阳极,这是造成局部腐蚀的根本原因。注入水中存在较高含量的氯离子和硫酸盐还原菌,加剧了腐蚀进程,造成油管腐蚀穿孔,形成了以FeCO3为主的腐蚀产物。建议加强渗氮油管质量管控,防止入井前渗氮层脱落,同时在注入水中加入杀菌剂减少细菌对腐蚀的影响,并在井下安装牺牲阳极短节预防腐蚀。

Several corrosion perforation spots are found on nitriding tubing of A2 well in Bohai S Oilfield during polymer injecting.In order to avoid corrosion failure again after replacing pipe string,the reasons for tubing corrosion failure of A2 Well is studied by corrosion morphology observation,corrosion products and corrosion medium analysis.It is found that the primary cause of local corrosion is parts of nitride case falling off and it forms anode of electrochemical corrosion.In addition,high content of Cl^- and sulfate reducing bacteria in injection water promotes corrosion,and it leads to corrosion perforation and forms corrosion products mainly in FeCO 3.This paper suggests that the quality control of nitriding tubing should be strengthened and nitride case falling off should be prevented before entrancing into well.Meanwhile,some bactericide could be added to injection water to reduce the effect of bacteria on corrosion,and sacrificial anode pup joint could be installed in the downhole to prevent corrosion.