Design And Analysis Of A Vibration Absorber Of Differential Pressure Type

Due to the formation and the bit’s structure,in oil drilling process the vibration of the drill string is inevitable.The vibration has a serious damage effect on drill strings and drill bit.What’s more,it will cause a low ROP.Therefore,it is meaningful to study on a new type of vibration reducer based on differential pressure.In view of the drill string vibration problem,based on the comprehensive comparison of various drill string shock absorbers,both of the model and the work principle of differential pressure type shock absorber was constructed,and the functions and loads for key parts in the absorber were given.By the differential pressure between the inside and outside of the shock absorber,it will generate a force on the piston’s surface.On one hand,the force will provide drill bit hydraulic thrust for drilling;On the other hand,the bottom drill string’s shake can be overcome by this hydraulic force,so it can consume the vibration energy,and the vibration will not pass to the upper drill string.Work capacity of the differential pressure type shock absorber was designed according to the common178 mm shock absorbers’ work.The design includes the nominal size,piston size and seal seat based on the load conditions.When bit pressure drop is 7MPa,the hydraulic WOB would be 283 kN.In practice,piston number would change to provide designed WOB.The mechanics model of the shock absorber is established under simplified conditions for the analysis of the placement of the shock absorber on drill string and the fatigue strength of some important parts.Factors that influence the reaction speed of piston are discussed with FLINET simulation.Combined with ANSYS WORKBENCH,the absorber’s vibration modal are studied with different stress conditions.According to the calculation,the dimensions meet the requirements of the maximum load strength and fatigue strength.Numerical simulation results show that the shock absorber pistons can response quickly.The deformation is small enough to ensure the shock absorber works stable under complicated situations.When the blot center hole diameter is 3 mm,the piston’s speed can reach 0.4 m/s.The absorber can work stability under different WOB.Its deformation can reach to 0.302 mm when its frequency is 360 Hz.Within 0~890Hz.When the frequency is 550 Hz,the absorber’s deformation can reach 24.7 mm,but it is still far less than the deformation corresponding to its natural frequency.So it can effectively avoid the generation of the drill string system’s resonance.