动静载荷比对钻齿破岩效率的影响研究

Effects of ratio of dynamic load to static one on rock-breaking efficiency

旋冲钻井技术能有效提高钻井效率,但由于对旋冲钻进时动静载荷比对破岩效率的影响认识尚不够清楚,使得旋冲钻井技术在推广应用时未能发挥其最佳性能。基于弹塑性力学和岩石力学,采用Drucker-Prager准则作为岩石的屈服准则,建立了钻齿-岩石互作用非线性动力学有限元模型,通过与实验对比验证了数值模型的可靠性,研究了载荷比对岩石内部应力分布规律及其对钻齿侵入岩石特性的影响。结果表明,动静组合载荷更有利于钻齿破岩;动静组合载荷总值恒定时,存在钻齿破岩效率最佳的载荷比,且其与岩石抗压强度正相关,围压为10～90 MPa时钻齿破碎灰岩的最佳载荷比为0. 42～0. 48。考虑到现有技术条件和工程实况,建议在灰岩地层进行旋冲钻进时载荷比取0. 1～0. 48。若其它目标地层的抗压强度大于或小于灰岩的抗压强度,可适当增大或减小载荷比。

Rotary percussion drilling technique can significantly improve the drilling efficiency.However,the best performance of this technique can’t be brought into play when it is popularized and applied due to our not enough understanding effects of ratio of dynamic load to static one on rock-breaking efficiency.Here,adopting Drucker-Prager criterion as the rock yield criterion,a non-linear dynamic finite element(FE)model of bit tooth-rock interaction was established based on the elastoplastic mechanics and the rock mechanics.The numerical simulation results were compared with test ones to verify the reliability of the numerical computation model.The effects of ratio of dynamic load to static one on rock internal stress distribution law and bit tooth’s penetrating rock features were studied.The results showed that the dynamic-static combined load is more beneficial for bit tooth’s breaking rock;when the total value of dynamic-static combined load is constant,there is a load ratio with the optimal bit tooth’s rock-breaking efficiency,it is positively correlated to rock compressive strength;the optimal load ratio for bit tooth’s breaking limestone is 0.42-0.48 when the confining pressure is 10-90 MPa;considering the existing technical conditions and engineering situations,the load ratio for rotary percussion drilling in limestone strata should be taken as 0.1-0.48;if the compressive strength of the other target strata is larger or smaller than that of limestone,the load ratio may increase or decrease appropriately.