Mechanical Analysis And Safety Evaluation Of Multi-packer String

Changes in temperature and pressure in the well will cause axial deformation of the string.However,for a string with packers,this axial deformation will translate into an axial force on the string when the packer is set in downhole,which,in severe cases,will affect the strength and safety of the string.Therefore,it is necessary to analyze and study the axial force and the axial deformation on the string section between each packer in order to ensure the safety of the downhole tubing string.Because of the string is a kind of statically indeterminate structure after the packer is set,it is not accurate to calculate the axial force and axial deformation on the pipe string segment by segment with the traditional formulas.Therefore,the multiple statically indeterminate structures of the packer string were fully considered in this paper,force method was used to analyze the mechanical properties of the three packers string at first,and the formulae for calculating the axial force and axial deformation of the two section strings between three packers under temperature effect and bulging effect were deduced.Then,mechanical analysis was performed on the four packers string using force method,and the formulae for calculating the axial force and axial deformation of the three section strings between four packers under the two effects were deduced.Finally,the mechanical analysis of multi-packer string was performed according to the analysis method and process of three packers and four packers tubing,and a general calculation model for axial forces of multi-packer string was established.Based on the calculation formula of the axial force and axial deformation of the string deduced in this paper,the error between the traditional calculation formula and the new calculation formula was analyzed,and the three,four,and five packers string were used as examples for analysis.Calculations prove that,the effect of pressure on string safety is greater than the effect of temperature on string safety;the effect of temperature on the axial deformation of the string is greater than the effect of pressure on the axial deformation of the string;the error between the two algorithms is only related to the length of the packer string section instead of the downhole temperature variation and the amount of pressure change in the wellhead,and the longer the length of string,the greater the error between the two algorithms;it will only affect the axial stress error and axial deformation error of the later string when the length of a certain string increases.In summary,the multi-packer string axial force calculation model deduced in this paper will help reduce the risk of multi-packer string accidents in the downhole,which can provide guidance on improved design and manufacturing of packer strings.