川东酸性环境中油管腐蚀分析及预防措施

Analysis and Preventive Measure for Tubing Corrosion in Acidic Environment of the East Sichuan

川东气田所属气井因井筒流体腐蚀含量高,井下油管被严重腐蚀破坏。腐蚀特征显示,油管腐蚀以电化学腐蚀为主,回注井还伴有细菌腐蚀。油管腐蚀井段从井口、上部、中部到下部各不相同,总体是油管外壁比内壁腐蚀严重;腐蚀形式为点孔腐蚀、坑点腐蚀和溃疡状腐蚀等;缓蚀剂加注及时及加注制度合理的气井,油管腐蚀较轻。引起川东地区油管腐蚀的主要因素包括流体性质、井筒有凝析液或井底有积液,油管材质选择不当、保护不及时等。在参考大量实际情况和实践应用基础上,根据油管腐蚀成因,推荐了优选抗硫耐蚀材料、安装井下封隔器、加注缓蚀剂、阴极保护等防腐措施。鉴于投运8a以上的气井油管有腐蚀断落的危险,投运5a以上的回注井油管有腐蚀断落的危险,应以此为参考,选择井下油管更换时机。建议加强不同环境油管腐蚀分析,为新井油管材质选择提供依据。

Because of high corrosion content of wellbore fluid,downhole tubing is damaged greatly by the corrosion in the gas wells of the east Sichuan gas field.Corrosion features show that tubing corrosion is elec trochemical erosion mainly as well as bacterial corrosion in the reinjection well.Corroded interval of the tub ing varies from wellhead,upper part,middle part to bottom part,and inside wall is corroded more seriously than the outside wall of the oil tube.The way of corrosion is point-pore corrosion,pit-point and ulcer-shape corrosion and so on.Weak tubing corrosion appears in the gas wells with inhibitor injection on time and rea sonable injection system.Main causes of tubing corrosion in east Sichuan are ：fluid properties,condensate liquid in wellbore or downhole fluid,and improper material and no protection timely of the oil tube.According to the tubing corrosion causes,the preferred sulfur corrosion resistant materials,installation of downhole packer,inhibitor injection,cathodic protection and other downhole tubing anticorrosion measures are recommend based on a large number of actual situation and application.There are risks of tubing corrosion collapse for the gas wells with 8 years production and the reinjection wells with 5 years production.Based on that,timing of downhole tubing change may be known.Tubing corrosion analysis should be strengthened for various environments so as to provide foundation for tubing material selection of new wells.