Study On Dynamic Simulation And Fatigue Characteristics Of Bias Unit In Point-to-the-bit Rotary

The mechanical internal bias pointing rotary guidance system can solve the low drilling efficiency,limited drilling depth,the smooth borehole,difficulty of drilling in horizontal and complex wells in slide steering drilling.The existing research results show that the offset mandrel is a weak link in the steering mechanism.In this paper,numerical simulation method is used to study the dynamics and fatigue characteristics of offset mandrel in an internal bias pointing rotary guidance system,which provides technical support for the design of the mandrel of the steering mechanism.Based on the existing experimental prototype,mechanical model of the spindle and bearing bias by using Solidworks and Ansysworkbench software was carried out,element type,material properties and mandrel constraint parameters were determined,and the stress,strain and deflection of the mandrel under static bias force are calculated.The dynamics simulation of the mandrel of the guide mechanism is carried out,the parameters of deflection angle,maximum stress and support force in the process of rotating bending are simulated under different deflections,and the results are compared with theoretical analysis,experimental research and static analysis,which provides a basis for design improvement.The fatigue curve of Ti alloy mandrel material was fitted in RecurDyn software.The fatigue life of the mandrel under the stress and strain level of the mandrel is calculated by choosing the relevant fatigue calculation principle and the stress history correction method.The fatigue life of the numerical simulation is analyzed and compared with the theoretical calculation and the experimental results and suggestions for the design of the offset mandrel are given.