渤海某油田井下管柱腐蚀失效分析及防护

Corrosion analysis and prevention of downhole string in Bohai A oilfield

渤海A油田动管柱修井作业期间,发现井筒故障率高,井下管柱严重腐蚀穿孔,甚至出现断裂落井的情况,给油田正常生产和现场作业带来极大困难。为探究油管腐蚀穿孔的原因,通过对油管材质、井筒液相环境以及腐蚀模拟实验等分析,表明该油管化学成分和洛氏硬度符合API5CT标准要求,腐蚀现象具有单一方向性,且腐蚀程度为中度腐蚀,腐蚀产物主要是碳酸亚铁(FeCO_(3))及硫铁化物。腐蚀的主要原因为油管材质中存在B类和D类非金属夹杂物,其局部位置在交变摩擦震动下受损引发点蚀,并在高硫化氢(H_(2)S)含量的井筒液相环境中进一步发生SRB细菌腐蚀及垢下腐蚀,从而导致油管穿孔断裂。针对该油田油管腐蚀原因及类型,针对性的开发出一种井筒完整性保护工作液BH-WZX01,其兼具缓蚀、阻垢和杀菌性能,可有效解决A油田现场井筒腐蚀问题。

During the workover operation of movable string in Bohai Oilfield A,the high wellbore failure rate was found,the corrosion and perforation of downhole string were serious,even that occurred fracture and fell in the well,which brought great difficulties to the normal production and field operation of the oilfield.In order to explore the causes of corrosion perforation,through the analysis of tubing material,wellbore liquid environment and corrosion simulation experiment,the results showed the chemical composition and Rockwell hardness of the tubing meet the requirements of API 5 CT standard.The corrosion phenomenon has a single direction,and the corrosion degree was moderate.The corrosion products were mainly ferrous carbonate(FeCO_(3)) and iron sulfides.The main reason of corrosion was that there were class B and class D non-metallic inclusions in the tubing material,and the partial positions pitting which caused by the damaged of alternating friction vibration,in addition,SRB bacterial corrosion and subscale attack occurred further in the wellbore liquid environment with high hydrogen sulfide(H_(2)S)content,resulting in perforation and fracture of tubing of tubing.According to the causes and types of tubing corrosion in Oilfield A,a wellbore integrity protection working fluid BH-WZX01 was developed.It has the properties of corrosion inhibition,scale inhibition and sterilization,that can solve the problem of wellbore corrosion effectively.