In Zaoyuan Oilfield and Wangguantun Oilfield of Dagang Oilfield Company, the wells feature large depth, high temperature, high water injection pressure, serious corrosion and scaling and complex wellbore conditions. The existing mechanical analysis software for tubing string in layered water injection is only capable of analyzing the axial force and axial deformation and checking the safety of strength under the lowering and lifting working conditions. Therefore, a mechanical analysis method for the multi-packer tubing string has been derived by comprehensively considering the constraint and impact of anchor tools and packers on tubing string deformation, the well deviation and orientation, the statical indeterminacy of the multi-packer tubing string as well as the impact of injected water temperature and expansion effect by injection pressure. The method is capable of analysis on the axial force, deformation and stress strength of each string segment of the layered water injection tubing string with two or more packers, and helps improve the accuracy of mechanical analysis of tubing string under different well conditions and working conditions. Case analysis shows that the analysis results can be used to guide the design of tubing string for layered water injection as well as to guide the research and development of auxiliary downhole tools such as layered water injection packers and anchor tools.

Packer is one of the most important downhole tools for successful multistage water injection. In order to understand the mechanical properties of packer setting components and key loading components, a commonly used Y341 packer was studied as an example by simulation mechanical analysis. A three-dimensional model of a full-size Y341 packer was established by SolidWorks software. The finite element analysis software was used to analyze the mechanical properties of key components such as setting piston, circulating piston, mandrel, and lock ring under different working procedures such as setting packer, water injecting and well circulating. Loading the three-dimensional model of the full-size Y341 packer by finite element analysis software, stresses, strains and deformations of each parts were analyzed corresponding to different working procedures. And then, the stresses, strains and deformations of each parts were compared and researched. Based on the analyses and researching, it was found that the stresses near threads, holes and seal grooves were larger due to stress concentration, under axial force, internal and external pressure. But the working stresses of each parts are smaller than part material yield strength during normal working procedures, confirming the requirements of down-hole tool operations. When moving upward under axial force, the contact force and stress between the setting piston and the outer sleeve is relatively larger. So, the design length of setting piston should be appropriately increased to increase the contact area between setting piston and the piston cylinder. When overcoming upward friction to move the circulating piston, the frictional shear stress at the front end is considerable. So, the design area of the front-end of circulating piston should be larger possibly. Due to the uneven force in contact areas between the mandrel and different parts affiliated, the stresses near holes and circulating are also concentrated. So, the design hole diameter should also be also larger possibly. The teeth of the lock ring near the loading end are the main load bearing parts. So, the strength of the lock ring's stressed end can be increased by changing the opening distance of lock ring, the tooth angle, and the number of the teeth. The simulation analysis is useful and helpful to understand the mechanical properties of key setting and loading parts, and provide a basis for improving the design of multistage water injection packer, especially reducing stress concentration.