高压井中套管缺陷对连接螺纹强度行为研究

Research on Strength Behavior of Casing Thread with Defects in High Pressure Wells

针对高压井套管缺陷对连接螺纹承载能力影响研究较少,套管安全评估依据不足的问题,以典型的APIφ177.8 mm×12.65 mm P110钢级的圆螺纹套管为研究对象,以弹性力学理论和腐蚀套管力学模型为基础,对不同腐蚀形态下套管-水泥环-地层有限元模型研究,分析了套管-地层-水泥环系统下套管螺纹牙的应力分布状态和3种腐蚀缺陷影响下螺纹连接部分的应力分布规律。获得了均匀腐蚀缺陷相对于低压井对高压井套管螺纹牙最大等效应力影响较大;点蚀与沟槽型腐蚀缺陷对套管螺纹牙最大等效应力影响变化相似;点蚀与沟槽型腐蚀缺陷发生在套管螺纹啮合段下段区域时影响显著;不同腐蚀缺陷下套管屈服的临界腐蚀缺陷深度等方面的认识规律。

There are few studies on the influence of casing defects on the bearing capacity of connecting threads in high pressure gas wells,and the casing safety evaluation cannot be supported by theory and data.Based on the above problems,the typical API 177.8 mm×12.65 mm P110 steel grade round threaded casing is taken as the research object.Based on the elastic mechanics theory and the corrosion casing mechanics model,the casing-cement ring-formation finite element model under different corrosion forms is established,and the casing thread tooth under the casing-formation-cement ring system is analyzed and studied.The stress distribution law of the threaded connection part under the influence of the stress distribution state and the three corrosion defects.The results show that the uniform corrosion has greater influence on casing thread maximum equivalent stress of high pressure wells than on low pressure wells;influence of pitting and groove corrosion defects on casing thread maximum equivalent stress effects were similar;pitting and groove corrosion defects in the bottom casing thread engagement segments exert significant influence.We also acquire the critical corrosion defect depth of casing under different corrosion defects.The research work in this paper provides a theoretical basis for safety assessment of casing threads in high pressure wells.