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 6617 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.