Simulation And Analysis Of Nonlinear Dynamic Characteristics Of Drill String In Coal Mine Directional Well

With the continuous improvement of coal technology,mine scale and coal mining depth,it is more and more important to effectively use directional well drilling technology to improve coal water disaster control.However,in the process of directional drilling in coal mine,the drill string is easy to be affected by various factors under complex working conditions,resulting in the quality and efficiency of the overall directional well engineering reduced.Therefore,the analysis and Research on the motion state and dynamic characteristics of the drill string is still the key problem to realize the accurate control of directional well trajectory.Firstly,based on the structural composition,working state and stress state of thedrill string in directional well,based on nonlinear dynamics,and considering the influence of boundary conditions and loads on the drill string,the drill string system is treated as an elastic beam element,and the vertical and horizontal torsional mechanical model and friction and collision model of the drill string in directional drilling are established The friction mechanism of sidewall reflects the movement characteristics of drill string system in directional well.Secondly,the effective tension,fatigue coefficient,torque and lateral force of drillstring in two directional wells are obtained by using wellplan software.The results show that the torque of drill string is the largest in the straight hole section of directional well,which is prone to drill string torsion accident;the drill string is prone to bending deformation and fatigue damage when it is in the state of large pressure in the deviation section;the data of drill string in bedding section is small,but the drill string near the bottom of the hole will appear obvious data sudden increase phenomenon,so the state of drill string at bit joint should be considered.By comparing the calculated data of two wells,it is concluded that the deviation radius of directional well is an important factor affecting the performance of drill string.Finally,the nonlinear dynamic characteristics of the drill string in the deviation section are analyzed by using the time center difference method in ABAQUS/EXPLICIT.The failure mechanism,motion law and mechanical properties of drill string in different curvature radius borehole are studied.From the simulation results,it can be seen that the smaller the deviation radius is,the greater the drill string strain is,and the more frequent the contact between the drill string and the borehole wall is,the greater the swing amplitude of each position of the drill string is in the drilling deviation making section;the smaller the deviation radius is,the greater the equivalent stress is,and the easier the drill string is to be bent;the smaller the deviation radius is,the greater the contact force between the drill string and the borehole wall is,and the more likely the drill string is to be worn.The research on nonlinear dynamics of drill string not only provides a theoretical basis for improving the service life of drill string and predicting and optimizing the well trajectory,but also provides strong technical support for reducing the occurrence of water disaster and promoting the safety production of coal mine.Figure[50]Table[3]Reference[80]...