宁夏盐池油田井下J55、N80套管腐蚀因素分析

Corrosion factors of J55 and N80 casing pipe in Yanchi oilfield,Ningxia

随着陆上油田相继进入开发的中后期,含水的上升,套损日益严重,其中CO2腐蚀是油气井套损的主要形式之一。宁夏盐池油田油层伴生气中CO2体积含量为4.7%~9.2%,现场出现了大量的腐蚀穿孔套损井,占全油田套损井总数的97%,严重影响了油田降本增效。为了充分掌握井下套管的腐蚀规律,现场采用连接油管的挂片器,开展了基于套管材质的井下挂片腐蚀实验,结合失重法以及扫描电镜(SEM)、能谱分析(EDS)、X射线衍射(XRD)等微观测试和分析手段,研究了井下环境中的J55、N80套管钢CO2腐蚀行为。结果表明,J55、N80套管钢腐蚀速率平均分别为0.0588 mm/a和0.0571 mm/a,属中等程度腐蚀,且以CO2局部点腐蚀-坑腐蚀为主,腐蚀产物主要为FeCO3。研究结果为指导油田制定合理的防腐措施提供了理论依据。

As land-based oilfields have entered the middle and late stages of development,water cuts have risen and casing pipe damage has become increasingly serious. Among them,CO2 corrosion is one of the main forms of oil and gas well casing damage. The CO2 volume content in the associated gas of an oil field in northern Shaanxi is 4.7% to 9.2%. A large number of corroded perforated casing damaged wells appeared on the site,accounting for 97% of the total casing damaged wells in the whole oil field,which seriously affected the cost reduction and efficiency increase of the oil field. In order to fully grasp the corrosion law of the downhole casing,a hanging device connected to the tubing was used on site to carry out the downhole hanging plate corrosion experiment based on the casing material. combining the weightlessness method with scanning electron microscopy( SEM),energy spectrum analysis( EDS),Xray diffraction( XRD) and other microscopic testing and analysis methods,the CO2 corrosion behavior of J55 and N80 casing steel in the downhole environment was studied. The results show that the corrosion rates of J55 and N80 casing steel are 0. 0588 mm/a and 0. 0571 mm/a,respectively,which are moderately corrosive,and mainly consist of CO2 local pitting corrosion-pit corrosion,and the corrosion products are mainly FeCO3.The research results provide a theoretical basis for guiding oilfields to formulate reasonable anticorrosion measures.