Research On Rock Breaking Law Of PDC Teeth Impact Based On Discrete Element

With the deepening of the mining depth,the mining speed becomes slower,and the difficulty of mining continues to increase.In order to increase the drilling speed,various types of torsional impactors are applied to PDC drill bits,but there is no theoretical basis,and the improvement of drilling efficiency is limited.Mastering the law of PDC bit breaking rock under impact is of great significance to improve drilling speed and economic benefits.In this paper,the basic principles of the discrete element method are systematically explained.The rock discrete element model is established through the establishment of a uniaxial compression model of rock and its parameters.And the full-bit drilling model is used to further study the rock breaking law under torsional impact conditions.Complete torsional impact laboratory experiments to verify the simulation results.The main research contents of this article are as follows:(1)The effects of four main parameters of the discrete element simulation model on the mechanical properties of the rock were analyzed through 16 sets of simulation experiments.By comparing with the indoor uniaxial compression experiment,the axial deformation of the rock failure-test force curve is almost the same,which proves that This improves the accuracy of the calibration parameters.(2)A discrete element model of PDC single-tooth cutting rock under torsional impact was established.The effects of cutting depth,cutting angle,cutting tooth diameter,different lithology and impact frequency on rock breaking efficiency were analyzed,and the conditions under torsional impact were determined.The optimal cutting depth is 2.5mm,and the optimal rake angle is 5 °.When satisfying the limitations of the existing process conditions and the constraints of different geological conditions,cutting teeth with smaller tooth diameters should be selected to improve drilling efficiency.(3)Based on the discrete element model of PDC single-tooth cutting rock,a discrete element model of PDC double-tooth cutting rock was established to verify that the two stress fields generated by the double-tooth movement of the PDC cutting tooth during the rock breaking process interfere with each other.It is determined that the minimum value of the crushing specific work under conventional drilling conditions is obtained at a tooth pitch of 5.5mm,and the minimum value of the crushing specific work under a torsional impact is obtained at a tooth pitch of 6.5mm,which provides a basis for scientific tooth layout.(4)Based on the discrete element model of PDC double-tooth cutting rock,a discrete element model of PDC full-bit drill for rock cutting is established,and cutting at different positions is determined by analyzing the axial force,torque and breaking specific work of cutting teeth at different positions The tooth force relationship provides a theoretical basis for the optimal design of the PDC bit under the condition of torsional impact.(5)Completed the full-bit rock breaking experiment under torsional impact conditions,and proved that the drilling speed is constant,the rock breaking efficiency under torsional impact conditions is much higher than that under a single condition.Rock-breaking efficiency will be more efficient than single hydrostatic drilling.By analyzing the impact curve of impact frequency on ROP,it can be seen that there is an optimal range of impact frequency that has reached the optimal ROP and improved rock breaking efficiency.