不同腐蚀缺陷套管剩余强度预测方法研究
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摘要
为预测在生产井套管腐蚀后的剩余强度,基于对套管表面腐蚀坑形状的规则化表征,采用有限元法建立了可模拟不同形状腐蚀缺陷的套管力学分析模型,用弹塑性理论进行腐蚀后套管剩余抗内压和抗外挤强度求解。以直径244. 5 mm、P110钢级套管为例,对圆球、椭球和矩体等3种形状、不同几何尺寸腐蚀坑的套管剩余强度进行规律性研究,给出了套管腐蚀后剩余强度预测流程,并成功应用于海外M油田在生产井。研究结果表明:腐蚀坑深度比是影响套管剩余强度的主要因素,随着腐蚀坑深度比的增加,套管剩余强度近似呈线性或6次多项式规律性下降趋势;当腐蚀坑投影面积相同时,矩体形坑腐蚀对套管剩余强度的影响最严重,椭球形腐蚀坑次之,圆球形腐蚀坑影响程度最低;对于相同的腐蚀形状及尺寸,腐蚀坑个数对套管剩余强度影响较小,但套管损坏或屈服的危险点增加。研究结果可为套管腐蚀后油气井的完整性及再利用评估提供有效手段。
To predict the residual strength of the corroded casing in production wells,based on the regularized characterization of the shape of the corrosion pit on the casing surface,a mechanical analysis model of casing that can simulate the corrosion pits with different shapes is established by using the finite element method. The residual burst strength and collapse strength of the casing are solved using elastic-plastic theory. Taking the φ244. 5 mm P110 casing for case study,the residual strength of the casing with different size of spherical,ellipsoid and rectangular pits was studied. The residual strength prediction process of the casing after corrosion was given,and was successfully applied to production wells of overseas M Oilfield. The results show that the corrosion pit depth ratio is the main factor affecting the residual strength of the casing. With the increase of the corrosion pit depth ratio,the residual strength of the casing decreases in approximately linear or the sixth-order polynomial trend. Given the same projected area of the corrosion pits,the corrosion of the rectangular pit has the most serious influence on the residual strength of the casing,followed by the ellipsoidal corrosion pit and the spherical corrosion pit. For the same corrosion pit shape and size,the number of corrosion pits has little influence on the residual strength of the casing,but increases the risk of casing damage or yielding. The study can provide an effective means for the integrity and reuse assessment of oil and gas wells with corroded casing.
To predict the residual strength of the corroded casing in production wells,based on the regularized characterization of the shape of the corrosion pit on the casing surface,a mechanical analysis model of casing that can simulate the corrosion pits with different shapes is established by using the finite element method. The residual burst strength and collapse strength of the casing are solved using elastic-plastic theory. Taking the φ244. 5 mm P110 casing for case study,the residual strength of the casing with different size of spherical,ellipsoid and rectangular pits was studied. The residual strength prediction process of the casing after corrosion was given,and was successfully applied to production wells of overseas M Oilfield. The results show that the corrosion pit depth ratio is the main factor affecting the residual strength of the casing. With the increase of the corrosion pit depth ratio,the residual strength of the casing decreases in approximately linear or the sixth-order polynomial trend. Given the same projected area of the corrosion pits,the corrosion of the rectangular pit has the most serious influence on the residual strength of the casing,followed by the ellipsoidal corrosion pit and the spherical corrosion pit. For the same corrosion pit shape and size,the number of corrosion pits has little influence on the residual strength of the casing,but increases the risk of casing damage or yielding. The study can provide an effective means for the integrity and reuse assessment of oil and gas wells with corroded casing.
引文
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[4]张智,孔维伟,刘志伟,等.腐蚀缺陷套管的剩余强度研究[J].中国科技论文,2016,11(21):2467-2472.ZHANG Z,KONG W W,LIU Z W,et al.Study on residual strength of corrosion defect casing[J].China Sciencepaper,2016,11(21):2467-2472.
[5]许志倩,闫相祯,杨秀娟,等.不同缺陷对套管剩余强度影响分析[J].机械设计,2014,31(8):74-78.XU Z Q,YAN X Z,YANG X J,et al.Different defects impact analysis on casing residual strength[J].Journal of Machine Design,2014,31(8):74-78.
[6]张西明,李军,张新发,等.长庆油田小套管的腐蚀与防护[J].腐蚀科学与防护技术,2004,16(1):59-61.ZHANG X M,LI J,ZHANG X F,et al.Corrosion and protection for small-casings in Changqing Oilfield[J].Corrosion Science and Technology Protection,2004,16(1):59-61.
[7]毛克伟,史茂成.油气井套管腐蚀原因与防腐措施[J].石油钻探技术,1996,24(1):31-36.MAO K W,SHI M C.Cause and prevention of casing corrosion in oilwells[J].Petroleum Drilling Techniques,1996,24(1):31-36.
[8]石油管材专业标准化技术委员会.含缺陷油气输送管道剩余强度评价方法:SY/T 6477-2014[S].北京:石油工业出版社,2015.Petroleum Pipe Professional Standardizatrion Technical Committee.Evaluation methods of remaining strength for oil&gas transmission pipeline with flaws:SY/T 6477-2014[S].Beijing:Petroleum Industry Press,2015.