| Rock burst is a common coal rock dynamic disaster in safe and efficient coal mine production,which has an important impact on coal mine production.For downhole rock burst disaster management,hole stress state while drilling sensing and dynamic inversion have always been a technical problem to be solved urgently.At present,there are also limitations on parameter adjustment in the drilling process,which leads to lag of LWD sensing and failure to realize real-time monitoring and dynamic inversion.In this paper,the drilling process is analyzed by numerical simulation method,and the PDC bit rock breaking simulation experiment system is developed based on Python language.The impact of rock breaking is analyzed and studied from the aspects of drilling parameters,and the feasibility of the test system and research results is verified through field experiments.The main research contents of this paper are as follows:(1)According to the mechanical properties of rock and the basic theory of discrete element,a two-dimensional discrete element model of rock was established with the help of PFC-2D software,and the process of rock crack propagation and failure was analyzed and studied.The analysis results show that the coal stress has little influence on the main crack during cutting.The stress changes with displacement in the process of drilling,and the stress changes periodically with the increase of displacement;The contact force between particles in the rock area in contact with the drill bit changes obviously,and there is obvious stress concentration.(2)By writing Python script,the parameterized modeling of PDC bit rock breaking model is realized,and the correctness of the system is verified by simulation.The research and analysis shows that: Due to the differences in rock characteristics;in the process of rock breaking by PDC bit,the drilling speed of bit gradually stabilizes within a certain range after reaching the peak value.At the same time,with obvious vibration phenomenon,the stress transfer changes dramatically.When other conditions remain unchanged,the drilling torque increases with the increase of stress in coal and rock mass.It is found that the size of the pit is different due to the random vinration and there is a compact area at the bottom of the pit.(3)Using the control variable method,according to the comparison calculation of experimental data and numerical simulation model,the influence law of drilling speed on torque is analyzed.It is concluded that the appropriate drilling speed has an important influence on the actual drilling process and the improving the rock breaking efficiency.When other conditions remain unchanged,the rock breaking efficiency of drill bit in the range of 0-250r/min decreases with the increase of rotational speed,and the rock breaking efficiency is the lowest when the rotational speed is 250r/min.When the rotational speed is greater than 250r/min,the rock breaking efficiency begins to gradually improve.The corresponding parameters are set and tested to verify the correctness of the conclusion obtained by numerical simulation analysis.Figure 53 Table 10 Reference 87... |
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