| Under the new trend of “deep,low,sea,unconventionality” exploration and development of oil and gas fields in our country,high efficiency rock breaking technology is very important.The rock breaking process assisted by axial impact load is based on the conventional rotary drilling,and the rock breaking efficiency is improved by using the impact load produced by the impactor.This technology is one of the main ways to speed up oil and gas drilling and has been widely recognized in the petroleum industry.However,there is still little research and lack of systematicness in the simulation experiment of percussion drilling condition,so there are still some deficiencies in rotary percussion drilling tools and drilling technology at present.In order to improve the experimental research of impact drilling,combined with the latest development in this field at home and abroad,the influence of axial impact load on rock breaking in PDC cutting is studied mainly by laboratory experiments and numerical simulation of rock breaking process.The mechanism of improving rock breaking efficiency of PDC bit by axial impact load is revealed in order to provide a reference for the further development and optimization of this technology.Firstly,according to the purpose and requirement of impact drilling experiment,a laboratory experiment system for rock-breaking drilling of PDC micro-bit with axial impact load is developed,and the different systems of the device are introduced.The test results show that the experimental system can successfully complete the rock breaking experiments in both conventional rotary drilling and axial impact drilling.Secondly,the influence of rotation speed,drilling pressure and impact load parameters on rock breaking of PDC bit is analyzed under the axial impact drilling mode by using the integrated experimental system of percussion drilling.The influence of axial impact load on rock breaking of PDC bit under different working conditions is clarified.Compared with conventional rotary drilling and axial impact drilling,the influence of axial impact load on stick-slip vibration of drill bit is analyzed.Through the analysis of cuttings particle size,the adaptability of rotary percussion drilling under different lithologic conditions is explored.The experimental results show that the same as the conventional rotary drilling,increasing the rotational speed and drilling pressure is beneficial to increase the mechanical drilling speed,axial impact load can restrain the stick-slip vibration of the drill bit,increase the impact force,and increase the rock breaking efficiency,increase the impact force and increase the rock breaking efficiency.Hard and brittle formation is more suitable for impact drilling.Finally,in the early stage of simulation,the rock material model for simulation is selected by uniaxial compression test and finite element simulation experiment.The rock breaking model of PDC cutting under axial impact load is established by using LS-DYNA simulation software.Then the rock breaking process of PDC cutting and rock damage process under impact load are simulated.The development and fracture evolution of cracks in rock under different loads are studied.The results show that axial impact load can promote the formation,development and penetration of cracks in the rock,increase the crushing volume and improve the rock breaking efficiency.Based on the combination of laboratory experiment and numerical simulation,the influence of axial impact load on rock breaking of PDC bit under different working conditions is clarified,and the influence mechanism of axial impact load on rock breaking of PDC bit is analyzed.The simulation experiment of percussion drilling condition is supplemented,which provides theoretical support for the establishment and optimization of the speed-up technology system of rotary percussion drilling in the next step. |
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