Analysis Of Factors Affecting Rock Breaking Efficiency Of PDC Bit By Rotary Percussion

Rotary impact technology has been paid attention to improve the rock breaking efficiency of hard formation,but it is not enough to excavate the rock breaking mechanism;The impact parameters adapted to formation parameters are not clear;The influence law of impact parameters is not clear,and there is no basis for the selection of impact parameters;The results show that the effect of tool acceleration varies greatly in different formations,regions and borehole diameters;The tool and impact parameters are selected randomly,and there is still a large space to improve the speed-up effect;At the same time,the comprehensive performance of the tool is poor,the service life is short,and the adaptability is not enough,so it is difficult to meet the complex working conditions and economic needs.Based on the finite element simulation,through the rock breaking process simulation model of single tooth and full-size bit,the stress state change law of different tooth shapes and different rock breaking methods is revealed;The single tooth simulation results show that the conventional tooth rock breaking is mainly shear failure;The tensile stress plays a decisive role in rock breaking;The impact action promotes the cutting teeth to eat into the stratum and the initiation and expansion of rock damage cracks.The full-scale bit simulation results show that the rock in front of the teeth is mainly subjected to tension and shear in the stage of impact force increase,and the rock in front of the teeth is mainly subjected to compression and shear in the stage of impact force decrease.Through the thermal mechanical coupling model of single tooth,based on multiple evaluation indexes of rock breaking efficiency,the influence of different tooth shape,impact load and impact frequency on rock breaking efficiency is explored.The simulation results show that with the increase of impact load and impact frequency,the penetration depth,crushing volume,maximum temperature and average temperature of conventional tooth,conical tooth and axe tooth increase rapidly at first and then tend to be stable,the specific work of rock breaking first decreases and then increases.Based on the rock breaking test data of rotary percussion,the rock breaking method of full-scale bit is established and verified.Through the full-scale rock breaking simulation model of bit,the effects of different tooth shape,rock type,impact load,impact frequency,WOB and rotational speed on rock breaking efficiency are explored.The simulation results show that with the increase of WOB,rotational speed,impact load and impact frequency,the bit ROP increases,and the WOB has the greatest effect on ROP;Changing the rock type and tooth shape not only changes the ROP,but also changes the law of ROP.