三元复合驱套管腐蚀原因及临界剩余壁厚研究

发布时间：2018-05-18 00:20

本文选题：临界剩余壁厚 + 腐蚀套管　；参考：《东北石油大学》2015年硕士论文

【摘要】：在石油开采过程中套管是地上与地下物质的重要交换通道。套管的服役条件非常苛刻,由于多种驱油方法的联合使用使得采出液成分十分复杂,正是这种理化环境复杂性使得套管失效现象频频出现,给油田的安全生产带来极大影响。本文针对大庆油田实际生产情况,对三元复合驱采出井的腐蚀损伤套管进行失效分析。通过对失效管段的宏观分析和微观分析发现腐蚀以内壁为主,附着有较厚的垢,垢下形成较多密集分布的腐蚀坑。严重的局部腐蚀特别是垢下腐蚀是套管失效的主要原因。通过对腐蚀介质的电导率、pH值及化学成分分析,了解了防垢剂及酸洗液可以加速腐蚀过程。最终确定套管的腐蚀机理为服役前期发生吸氧腐蚀,服役过程中管壁结垢发生严重的垢下腐蚀直至穿孔,在腐蚀过程中,酸洗液中的H+、Cl-及防垢剂直接加速了腐蚀。结合腐蚀机理及局部腐蚀的失效形式,利用ANSYS有限元软件重点模拟了平底方形、平底长圆形、椭圆形、圆形蚀坑及组合腐蚀缺陷的几何尺寸及内压对失效的影响,其中腐蚀深度和内压对临界剩余壁厚的影响最大,缺陷长度及缺陷宽度的影响依次降低。对于圆形点蚀坑,当深度超过7mm时,等效应力最大值会出现明显的激增。对于双点腐蚀而言,本文分别模拟了平底方形及长圆形腐蚀缺陷,并得到两类缺陷相互干涉距离分别为90mm和115mm。此外,通过对含腐蚀缺陷套管的室内模拟打压实验,并将实验数据与ANSYS软件模拟数据进行对比,得到两者的最大误差为7.75%,符合工程应用中小于10%的要求,验证了有限元分析方法的准确性。最后,结合Ansys Workbench软件中的优化设计模块,进行了二次开发,进而更方便的计算腐蚀套管临界剩余壁厚,为剩余寿命的预测奠定基础。
[Abstract]:In the process of oil production, casing is an important exchange channel between ground and underground material. The service conditions of casing are very harsh, because of the combined use of many oil displacement methods, the composition of produced liquid is very complex. It is precisely this kind of physical and chemical environment complexity that makes casing failure frequently appear, which has a great impact on the safe production of oil field. According to the actual production situation in Daqing Oilfield, the failure analysis of corrosion damaged casing in ASP flooding production wells is carried out. Through the macroscopic and microscopic analysis of the failure pipe section, it is found that the corrosion is mainly on the inner wall, and there is thicker scale attached to it, and more dense corrosion pits are formed under the scale. Serious local corrosion, especially scale corrosion, is the main cause of casing failure. Through the analysis of pH value and chemical composition of the corrosion medium, it is understood that the corrosion process can be accelerated by the scale inhibitor and acid lotion. Finally, it is determined that the corrosion mechanism of the casing is oxygen absorption corrosion in the pre-service period, serious corrosion under the scale of the pipe wall and even perforation in the service process. In the process of corrosion, the H _ (+) Cl- and anti-scaling agent in the acid washing liquid directly accelerates the corrosion. Combined with the mechanism of corrosion and the failure form of local corrosion, the effects of geometric dimension and internal pressure of square, oblong, elliptical, circular pits and combined corrosion defects on the failure are simulated by ANSYS finite element software. The influence of corrosion depth and internal pressure on critical residual wall thickness is the greatest, and the influence of defect length and defect width decreases in turn. For circular pitting pits, the maximum equivalent stress increases significantly when the depth exceeds 7mm. For double point corrosion, the square and long circle corrosion defects with flat bottom are simulated, and the interference distance between the two kinds of defects is 90mm and 115 mm respectively. In addition, by comparing the experimental data with the simulation data of ANSYS software, the maximum error is 7.75, which accords with the requirement of less than 10% in engineering application. The accuracy of the finite element analysis method is verified. Finally, combined with the optimization design module in Ansys Workbench software, the secondary development is carried out, and the critical residual wall thickness of corroded casing is calculated more conveniently, which lays a foundation for the prediction of residual life.
【学位授予单位】：东北石油大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TE983

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