超深高温高压气井完井含伸缩管测试管柱的应力与变形特征

塔里木盆地MJ4井测试管柱长6 617 m,测试时井底压力为101.63 MPa,完井作业过程中管柱出现了塑性变形问题,迫切需要准确地确定管柱塑性变形究竟发生在完井作业的哪个阶段。为此,采用三维有限元分析方法,结合MJ4井坐封、压裂和试油3个典型的载荷工况,对管柱的变形和轴向应力分布进行了数值计算,总结了含伸缩管的完井测试管柱力学行为计算流程。研究内容主要包括:①提出了具有伸缩管的油管柱系统中伸缩管的伸长与闭合状态的判断依据,并给出了相应的计算原理和计算公式,计算了MJ4井油管柱伸缩管的伸长—闭合状态;②给出了水力锚咬合不良产生的封隔器环空附加压差载荷的分析计算方法,模拟了其对管柱系统变形行为的影响,指出了附加压差载荷对管柱的塑性屈曲变形有着重要的影响;③计算模型引入了侧向屈曲变形的限制,从而间接考虑了接箍刚度对屈曲变形的影响,计算分析了油管柱在各种载荷共同作用下的变形情况,得到的数值结果显示与观察到的变形现象相同。研究结果表明,MJ4井管柱的塑性变形发生在压裂改造施工阶段,各种形式的液体压力载荷及重力载荷是塑性变形的主要原因。结论认为,含伸缩管测试管柱的力学计算模型可作为优化施工和管柱系统结构设计的重要理论工具和分析手段。

Stress and deformation characteristics of completion and testing tubing string with expansion joints for ultra-deep HTHP gas wells

In Well MJ4, Tarim Basin, the testing tubing string is 6 617 m long and the bottom-hole pressure during the testing is 101.63 MPa. During the completion job, plastic deformation occurs in the tubing string, so it is very necessary to figure out at which stage of the completion job plastic deformation occurs on earth. For this reason, the three-dimension finite element analysis method was used to perform numerical calculations for the deformation of tubing string and the distribution of axial stress based on three typical load conditions (setting load, fracturing load, and well testing load of Well MJ4); a process for calculating the mechanical behavior of a completion and testing tubing string containing an expansion joint was then developed. The study content mainly includes: (1) A criterion was developed to determine the extension and closure status of the expansion joint in the tubing string; corresponding calculation mechanism and formulae were provided; and the extension–closure status of the expansion joint in the tubing string for Well MJ4 was calculated. (2) A method was developed for analyzing and calculating the additional pressure difference load in the packer annulus caused by poor engagement of the hydraulic anchor; the impact of the additional pressure difference load on the deformation behavior of the tubing string was simulated; and the significant impact of the additional pressure difference load on the plastic buckling deformation was figured out. (3) The limit of lateral buckling deformation in a calculation model was introduced, and so the impact of collar rigidity on the buckling deformation was indirectly considered; the deformation under the joint action of all loads of the tubing string was calculated, and the numerical result was the same as the observed deformation. The study results show that the plastic deformation of the tubing string for Well MJ4 occurs at the fracturing stage and the major causes are hydraulic pressure loads and gravity loads in different forms. The conclusion shows that the mechanical calculation model of the testing tubing containing the expansion joint can be used as an important theoretical tool and analysis approach in optimizing operations and designing the tubing string structure.