Parametric sensitivity study on bit pulling simulation in horizontal wellbore of coal seam

Introduction To enhance the safety and efficiency of coalbed horizontal well construction, this study addresses abnormal increases in pull-back resistance and drilling tool damage caused by the random accumulation of residual cuttings beds during deep and mid-deep coalbed extraction. Methods A discrete element simulation software (EDEM) was employed to develop a bit pull-back simulation model for horizontal well sections. Using variables such as cuttings particle size, accumulation morphology, and pull-back parameters, orthogonal experiments were designed. Parameter sensitivity was analyzed through intuitive analysis and variance analysis to investigate the coupled effects of multiple factors on bit pull-back torque and force. Results The results indicate that cuttings beds influence pull-back mechanical responses through three mechanisms: particle friction, mechanical obstruction, and accumulation disturbance. Among these, cuttings particle size exerts the most significant impact on torque and pull-back force. Specifically, the peak torque and peak pull-back force for 20 mm cuttings increased by 4 times compared with those for 10 mm cuttings, with notably amplified mechanical parameter fluctuations under larger particle sizes. Discussion Other factors, such as accumulation height, showed secondary effects on both torque and pull-back force. Bit rotational speed exhibited a secondary effect only on torque, while some minor factors exerted negligible influences on both torque and pull-back force.