| The actual production results show that,after the centralizers are installed below the neutral point,the eccentric wear phenomenon still exists above the neutral point even in the whole well Obviously,the static buckling theory of the rod string below the neutral point in the cylinder can not explain the actual eccentric wear phenomenon in the whole well.The static buckling theory of rod string in the cylinder still has great limitations According to the structural and mechanical characteristics of sucker rod string,the static buckling theory of rod string in the cylinder is further improved in this paper.Further,the transverse vibration law of sucker rod string with buckling displacement excitation and its eccentric wear law of rod-tubing collision are studied for the first time.Then the optimization design method of centralizer layout based on the simulation of buckling configuration and the transverse vibration is formedConsidering the influence of couplings and centralizers local hydraulic resistance,the longitudinal vibration wave equation of sucker rod string with nonlinear damping is established,and the numerical simulation model of nonlinear wave equation is established based on difference-numerical integration.Further,the simulation method of axial distribution load of sucker rod string based on nonlinear wave equation is formed.The simulation results show that the axial distribution load has obvious non-uniform distribution characteristics with time and well depthTaking the whole multistage rod string with the non-uniform axial distribution load as the research object,the method for the eccentric wear critical load of rod-tubing is established,which can be used in a wider range.It is pointed out that the combination of rod string,rod length and non-uniform axial distribution load has great influence on the critical load of eccentric wear.Further,the simulation model of dynamic buckling critical condition of entire sucker rod string is established,and the dynamic buckling critical load is solved.The simulation models of three-section,four-section and five-section space buckling configuration are established respectively for the entire rod string in the vertical cylinder,which are composed of many nonlinear algebraic equations consisting of the high order variable coefficients ordinary differential equation and the boundary and continuity conditions.The Runge-Kutta numerical method is used to solve the above differential equations,the boundary and continuity condition as the constraint condition,then the simulation method of least square method based on initial values each section is established.The difficult problem of system simulation is solved and the overall numerical simulation for buckling configuration is realized.Further,Based on the three-section buckling configuration of two adjacent rod strings with local radial constraints,the simulation model of the entire rod string space buckling configuration is established considering the influence of local radial restraint of the couplings and centralizers.So,the simulation analysis method of eccentric wear area and contact pressure of rod-tubing is formed based on buckling configuration simulation of sucker rod stringIn view of the fact that the entire sucker rod string equipped with centralizers is still in the buckling state,the buckling configuration of sucker rod string during the down stroke is taken as the displacement excitation of the transverse vibration.Considering the influence of axial distribution load along the well depth and time on the transverse vibration,a nonlinear transverse vibration simulation model for sucker rod string in the tubing is established.Therefore,the simulation analysis method of eccentric wear of rod-tubing based on the simulation of transverse vibration and collision law of sucker rod string is formed.At last,a new optimization design method of centralizer layout is formed based on the simulation of rod string transverse vibration and the collision force of rod-tubing. |
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