Mechanics Analysis And Simulation Of The Spindle Of The Point-the-bit Steering Drilling Tool

Along with the oil and gas exploration becoming harder and harder, especially with the development of unconventional gas field in recent years, directional drilling technology is becoming the mainstream technology. As a kind of infinite adjustable hole trajectory control tool, the point-the-bit steering drilling tool can save drilling time effectively and improve the efficiency of drilling. The mechanical behavior of the spindle is related to the design and control of borehole trajectory, drilling parameter optimization and structure optimization of the tool. Therefore, It is important of mechanics analysis and simulation of the spindle.Based on the drill string mechanics and finite element theory, this paper simplified the spindle of the point-the-bit steering drilling tool and set up the theoretical model of it. The statics mechanical model had been established by the vertically and horizontally bent law and the influence of the shell stiffness, spindle stiffness and the structural parameters of tool to the deflection and angle of spindle. By using the method of multi-objective optimization, the structure parameters of the spindle have been analyzed. The dynamics simulation model of the spindle has been established by finite element method and the affecting factors to the mechanical behavior of the spindle have been researched, such as the dynamic displacement, drilling pressure, torque and vortex. The critical speed of the spindle has been researched by the modal analysis theory. Finally, fatigue life of the spindle has been studied by combining the theory of fatigue life. Summarizing the research work of this paper, it the main achievement of this research is as follows:(1) The research purpose and current research status of the spindle mechanical behavior of the point-the-bit steering drilling tool have been summarized and a research method of combining the theoretical research and finite element have been put forward.(2) The basic structure and working principle of the point type steering tool have been introduced and the statics mechanical model had been established. The mechanical optimization analysis of the spindle has been researched.(3)The dynamics simulation model of the spindle has been established by finite element method and the affecting factors to the mechanical behavior of the spindle have been researched, such as the dynamic displacement, drilling pressure, torque and vortex. The critical speed of the spindle has been researched by the modal analysis theory.(4) Finally, the spindle has been modeled by using three-dimension solid element and the fatigue life of the spindle in the down hole conditions has been researched.According to the research contents, the main research results of this article are as follows:(1) The statics mechanical model has been established which the shell stiffness has been considered and the deflection equation, Angle equation and constraint force equations of the bearings have been established. Based on the statics mechanical model, the influence of structure parameters on the bearing constraint reaction force, eccentric ring constraint reaction force and the bending load of the bearing have been researched. Taking bearing constraint reaction force and eccentric ring constraint reaction force as objective function, the parameters of the spindle of the point-the-bit steering drilling tool are optimized. Based on the optimization results, the matching scheme of the bearing, eccentric ring, the position of the eccentric ring and the spindle length in different situations have been studied.(2) Based on the theory of elastodynamics, the vibration equation of the spindle is deduced by using the Hamiltonian method. The vibration mechanism of the spindle under the effect of lateral force and torque has been established through the vibration equation. By using finite element method, the spindle has been divided both in space and in time and the stiffness matrix and mass matrix and the damping matrix of the spindle have been established. The theoretical method of studying the spindle dynamics by using the finite element method has been elaborated. The relationship between displacement and the angle of the eccentric have been researched and the geometric boundary conditions of finite element simulation analysis have been given. By the means of finite element software, the dynamic simulation of the spindle has been conducted and the simulation results have been compared with the results of simulation test which verified the correctness of the simulation data. The simulation results show that the drilling pressure and spindle rotating speed have little effect on the mechanical behavior of the spindle and eccentric displacement have significant effect on the mechanical behavior of the spindle which present the linear increase trend.(3) Based on the theory of elastic mechanics and structural dynamic equation, the basic structure of the free vibration eigenvalue problems is studied and the vibration equation in the condition of zero damping and free of external load free. Based on the ANS YS software, the finite element mode of the spindle has been established by using the BEAM 188 element and the bearings have been simplified by using the COMBI214 element. The calculation results show that the first-order natural frequency of the spindle is 19.074 HZ and the vibration type of the spindle was manifested as first-order lateral vibration. Combined with modal analysis results, it is concluded that the critical speed of the spindle is 1144.44r/min which has large difference with the designed rotational speed of it which is 200r/min. The results verify the safety of the spindle when it works.(4) Combined with the static and fatigue module of ANSYS, the simulation research of the spindle has been conducted and the Goodman theory has been applied for the mode correction. The simulation results show that the maximum alternating stress of the spindle generated at the position of the self aligning bearing which is 272.8MPa. Based on the S-N curve of the material of the spindle, the cycle times of alternating stress has been interpolated which is 107 and it can satisfy the design requirements.The article research results provide a dynamic method for design and simulation of point-the-bit steering drilling tool and play a guiding role in designing of borehole trajectory control, drilling parameter optimization and structure optimization of the tool.