Research Of Mechanical Analysis And Application Of Downhole Operation String In Horizontal Well

The downhole operation string of horizontal well bears complex forces,and it is difficult to judge the actual stress situation of string only through changes of wellhead load.Therefore,the construction safety and construction quality are of great uncertainty.This thesis studies on the force condition of the string during the process of downhole operation in horizontal well.The process of downhole operation is divided into three parts: tripping in string,tripping out string and the construction stage.The analysis the stress condition of the string is accordingly based on the above three processes.In the thesis,the type of operation includes oil testing,fracturing,flowing back,drilling out,milling,sand washing and fishing.Corresponding to the conditions above,this thesis researches on the forces that the string suffered such as gravity,hydraulic pressure,reaction forces between string and casing,viscous force and friction from working fluid.The thesis establishes the force calculation model of the operation string for the vertical section,inclined section,bending section and horizontal section of wellbore and realizes the calculation of load,axial deformation and the string intensity check.The thesis studies on the piston effect,helical buckling effect,temperature effect and ballooning effect of the operation string in horizontal well.The thesis also discusses some abnormal conditions in horizontal wells construction,such as broken string and packer failure and establishes the optimization methods of string structure and combination.The thesis also provides construction parameters design method and stress analysis of example wells in field operations by using the calculation model established in the paper.Generally,the study provides basis and means of optimization for safety construction and therefore guarantees success rate of horizontal well construction.