瞬态力—热耦合作用下套管应力影响因素分析

Effects of Multi-factor on Casing Stress Under Transient Thermal-mechanical Coupling

页岩气井压裂过程中出现的套管变形问题已经成为制约我国页岩气高效开发的重要因素。在页岩气水平井固井时常出现套管偏心现象,且页岩气井压裂改造次数多、井下温度场变化大,套管承受复杂的交变载荷。基于此建立套管偏心情况下的力-热耦合模型,分析了注液温度、压力、排量等因素对套管应力的影响。计算结果表明:压裂过程中,套管温度先迅速降低,然后逐渐稳定;套管内壁最大应力随偏心角的增大而增大;注液温度越低,井底温度下降越快,导致套管最大应力增大;在力-热耦合条件下,套管内壁的最大应力随着压力的增大而增大;排量增加,传热系数增大,套管最大应力也随之增大。

The casing deformation problem in shale gas wells has become an important factor that restricts the efficient development of shale gas.In the shale gas reservoir,casing eccentricity often occurs during casing cementing.In addition,the fracturing time is longer,and the downhole temperature field changes greatly during later reservoir reconstruction.Therefore,this paper establishes casing eccentric thermal-mechanical coupling model,and analyzes the effects of injection temperature,internal pressure and displacement on the instantaneous stress of casing.Results indicate that the casing temperature decreases rapidly to nearly constant temperature during fracturing.The maximum stress of the inner wall of the casing increases with the increase of the eccentricity angle.The lower the injection temperature,the faster the bottom hole temperature decreases,resulting in an increase in the maximum casing stress.Under thermal-mechanical coupling conditions,the maximum stress on the inner wall of the casing increases with pressure increasing.The heat transfer coefficient increases with the increase of displacement,and then the maximum stress of the casing also increases.