Dynamic Characteristics Analysis And Optimization Of Drill String System In Coal Mine Horizontal Well

Horizontal well drilling technology has obvious advantages in coalbed methane development and gas detection,and has been rapidly developed and applied in the current coal mining field.In the drilling process of horizontal well,the multi-directional friction collision between drill string and well wall is more complex,which makes the drill string failure more easily.At present,the mechanism of drill string vibration on the failure of horizontal well drill string is not clear,especially in the case of downhole accidents such as sticking,the modal characteristics of drill string under the action of propulsive force,pulling force and torque,and the variation law of vibration characteristics of drill string system when drilling to different depths need to be clarified.Based on this,this paper takes the horizontal well drill string system as the research object,analyzes the influence of drill string structure parameters and operating parameters on the modal characteristics of the drill string system,discusses the transient dynamic characteristics of the drill string system under different drilling parameters,and optimizes the dynamic characteristics of the drill string system by using the torsional impact method.The main contents of this paper are as follows:(1)On the basis of reasonable simplification of horizontal well drill string system,considering the comprehensive effect of external load and well wall constraints on drill string,the substructure method is used to construct rock-bit substructure and drill stringwell wall substructure.The random collision theory and dynamic gap element method are used to describe the internal interaction of the substructures.The substructures are integrated into a complete dynamic model of horizontal well drill string system through interface coordination condition;(2)Considering the support and restraint effect of the horizontal well wall on the drill string,the structural parameters such as the length,cross-section shape and wall thickness of the drill string are analyzed,as well as the influence law of the propulsive force,pulling force,torque prestress accumulated in the drill string on the modal characteristics of the drill string system in case of downhole accidents such as sticking,which is helpful to select the structural parameters of the drill string and avoid resonance phenomenon;(3)By using the finite element method,the transient dynamic simulation of the drill string system in the process of drilling is carried out,and the influence of drilling depth,input WOB and drill string speed on the vibration characteristics of the drill string system in the longitudinal,transverse and torsional directions is studied,so as to provide the basis for the optimization of the process parameters in the horizontal well drilling process;(4)Based on the analysis results of the dynamic characteristics of the drill string system in horizontal well,the torsional impact method is used to optimize the dynamic characteristics of the drill string system,improve the vibration characteristics of the drill string in the longitudinal,transverse and torsional directions,and improve the fatigue life and drilling speed of the drill string.In conclusion,the research in this paper has a certain guiding role for the dynamic characteristics analysis and optimization of the drilling string system in horizontal wells,the matching of drilling process parameters,the avoidance of harmful vibration,and the improvement of the service life of drilling tools.