超深井非均匀地应力场中射孔套管强度分析

Analysis of Perforated Casing Strength in Non-uniform In-situ Stress Field in Ultra-deep Wells

针对非均匀地应力、内压、射孔耦合作用下超深油气井试油和生产过程中经常出现的射孔套管损坏问题,采用有限差分软件建立了射孔套管-水泥环-地层三维地质模型,分析了射孔、内压以及非均匀地应力对超深井射孔后套管强度的影响。研究表明,射孔套管的剩余强度低于未射孔套管的剩余强度;射孔改变了套管应力的分布状态,射孔后套管最大应力发生在射孔处,孔眼处局部应力增大;射孔套管等效应力随内压的增加先降低后增加,存在一个临界值;当套管受非均匀地应力作用时,套管等效应力和变形量增大,且随着应力比的增加,套管等效应力和变形量随之增加,套管更容易发生损坏。该研究为套管的设计和应用提供了理论依据。

To alleviate the problems of casing collapse induced by the coupling effect of non-uniform in-situ stress,internal pressure and perforating during oil and gas well testing and production process in ultra-deep wells,a 3Dfinite difference model with perforated casing,cement and formation was established.The effect of perforating,internal pressure and non-uniform in-situ stress on casing strength in the non-uniform in-situ stress field in ultra-deep well was simulated by using the model.The result indicates that the residual strength of perforated casing is lower than that of non-perforated casing,Perforating changes the stress distribution of casing,and the maximum stress of perforated casing is near the perforating position.The local stress near the bullet hole increases.The equivalent stress on perforated casing decreases till a minimum value and then increases when the internal pressure increases,Under the effect of non-uniform insitu stress,a larger stress ratio results in greater equivalent stress and deformation on casing,which would cause the casing more prone to be damaged.It provides a theoretical basis for the casing design and application.