| Percussive drilling technology is a prevalent drilling technology which can greatly improve drilling efficiency.It is an effective method to improve the drilling efficiency of deep wells,ultra-deep wells and hard formations,and reduce the cost of rock drilling.Therefore,it has broad application prospects.Percussive drilling technology is generally used in conjunction with PDC bits,which can effectively improve the cutting performance of PDC bits,alleviate stick-slip vibration during drilling and effectively exert the advantages of PDC bits in shear rock breaking,additionally,improve the.rock breaking efficiency in hard formation.However,due to insufficient research on rock breaking mechanism,the rationality of popularization and application of percussive drilling technology need to be improved.Most field feedbacks on its working parameters are still based on using experience,without specific theoretical basis.This cannot give full play to its optimal rock breaking efficiency,which not only inhibits the acceleration effect of percussive rock breaking tools,but also hinders the acceleration of products upgrading and tools promotion of percussive rock breaking.At present,the research focuses of many petroleum scholars from domestic and oversea are still on the development of new percussive drilling tools.The tools' working principles and characteristics are studied,while the most basic research on the mechanism of rock breaking and speed-up are neglected.Among the existing rock-breaking technologies,rotary-percussion drilling technology has developed earlier,and there are many relatively studies on its rock-breaking mechanism from domestic and oversea.The studies mainly focus on the verification of the speed-up effect compared with conventional rock-breaking methods,but lack of researches on the impact of various working parameters on rock-breaking efficiency and the state of bit movement under rotary-percussion drilling method.Rock-breaking by torsion impact is a rising technology in recent years,the experts and scholars about it are relatively scarce in domestic and oversea;mainly focusing on its effectiveness analysis of restraining stick-slip vibration of drill bits but lack of relevant research on rock-breaking mechanism and the influence of working parameters on rock-breaking efficiency;composite impact rock-breaking technology,as a new rock-breaking technology,has not yet been put forward by experts and scholars at home and abroad on its mechanism of rock-breaking speed-up.The study of surface.The study of rock breaking speed-up mechanism and rock breaking efficiency under different working parameters is of great significance for deepening the understanding of rock breaking speed-up mechanism and providing theoretical basis for the selection of design parameters and working parameters of various percussive drilling tools.The main research work of this paper is as follows:(1)According to the existing knowledge of rock fragmentation mechanics,combined with the research of PDC bit-rock contact model,the rotary cutting response model of PDC bit is obtained,and compared with the experimental results of other people,the cutting characteristics of PDC bit under multi-load are determined theoretically.(2)Based on the theory of rock mechanics and damage mechanics,Drucker-Prager criterion is selected as the elastic-plastic constitutive relation of rock and equivalent plastic strain as the failure criterion of rock material.The non-linear dynamic three-dimensional model of full-scale PDC bit dynamic rock breaking is established by finite element method.The drilling process and rock breaking process of PDC bit under non-impact,axial impact,torsional impact and combined axial and torsional impact are analyzed respectively.(3)By comparing with the conventional drilling method without impact load in the process of rock breaking,such as the principal stress of rock unit,the motion and vibration of bit and the damage law of rock unit,the acceleration mechanism of rotary breaking and torsional breaking is revealed.(4)The influence of working parameters such as impact frequency,impact load,bit speed and rock properties on rock breaking efficiency under rotary and torsional breaking is calculated and analyzed,which provides a theoretical basis for the design parameters and working parameters of impact drilling tools.(5)Analyzing and comparing the rock breaking efficiency of composite impact under different combination of axial impact frequency and torsional impact frequency,it is concluded that the combination of low-frequency torsional impact and high-frequency axial impact has higher rock breaking efficiency.At the same time,by comparing with rotary breaking rock and torsional breaking rock,it is concluded that the composite impact breaking rock technology solves the formation limitation of rotary breaking rock and the abrasiveness of PDC bit of torsional breaking rock. |
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