Research And Improvement Analysis On The Mechanical Behavior Of Key Thread Joints Of Screw Drilling Tools

With the continuous development of drilling technology and crafts,the Positive Displacement Motor(PDM)has been widely used in drilling engineering because of its high efficiency of auxiliary rock breaking and wide adaptability,but the fatigue failure of PDM is gradually becoming a very prominent problem.The key parts of the thread load situations are very different,resulting in a large difference in safety factors,so that will arise the situation with a big different fatigue life,resulting that some parts of the residual fatigue strength of life is still very long while others parts have been fatigue damage,greatly increasing the cost of drilling.As the PDM is mainly used for drilling engineering in the orientation,making oblique,so the main part of the load to bear roughly three categories:axial load,torque load,bending moment load.Since the screw drill is in the bottom of the wellbore,near the drill and the drill rotation and other reasons,these three types of loads are followed by random vibration laws of the fluctuating load,its size and direction changes with time,easily lead to thread tripping,fatigue failure problem.In this paper,after analyzing the key parts of the screw drilling rigs,the fatigue life of the key screw joints is calculated and the calculated results are compared with the fatigue life calculation.The specific work is as follows:1.The research on the mechanical behavior of thread and status of thread fatigue theory and simulation at home and abroad;2.Based on the understanding of the advantages of each software,the analysis module and the analysis process,the simulation model of the key part of the PDM was established by using ABAQUS ’strong nonlinear simulation ability;3.The mechanical behavior of the screw thread under the axial load,the torque load and the moment load is studied.The mechanical analysis of the influence of the load parameters on the mechanical behavior of the screw is carried out;4.Based on the comparison of the fatigue test data of a company,the FE-safe fatigue simulation software was used to quantitatively analyze the fatigue life of the simulation model based on the simulation results of ABAQUS simulation.On the basis of fatigue analysis,the structural parameters of the screw shaft of the PDM and the screw joint of the stator shell are optimized.In this paper,the mechanical behavior of the screw thread under different loads is studied systematically.Based on the analysis of its fatigue life,the structural optimization is completed,which provides a scientific basis for improving the working life of the screw drilling machine.Reducing the fatigue failure of the screw drill has a very important engineering value.