| PDC bits are widely used in drilling engineering for its high penetration rate, long life, and flexible features. Torsional impact drilling technology expands the scope of PDC bits, It can effectively eliminate stick-slip vibration phenomena during PDC bits drilling in hard formations with high rock breaking efficiency. While the torsional impact drilling assembly must be equipped with a dedicated PDC drill bit in order to improve rock-breaking efficiency. Because people does not deeply understand the rock breaking mechanism of torsional impact drilling, lead to unreasonably design and selection PDC bits and drilling parameters, thus can not improve rock breaking efficiency with the torsional impact drilling assembly. PDC cutter as a cutting unit to PDC bits is a key element of the present study, it is also the foundation of PDC bit performance analysis. A series of numerical simulations were carried out in order to observe the cutting process under torsional impact drilling and conventional rock drilling.(1) Research on the status and application of relevant domestic and foreign PDC drill bits and cutter rock-breaking to start research study to determine the content, purpose and methods.(2) A three-dimensional (3-D) nonlinear dynamics simulation model of rock breaking with a PDC cutter was established to analyze the variation of Mechanical Special Energy (MSE) required to cut rock by varying parameters:confining pressure, the back and side rake angles, cutting parameters and other factors. Verifying the correctness of the results of the numerical simulation by compared the simulation results to experimental results of previous studies.(3) Research torsional impact rock breaking mechanism wih the PDC cutter angular velocity, torque, breaking volume of rock, Mechanical Special Energy, failured mode of rock elements. Analyze the variation of MSE of torsional impact by varying parameters:the back rake and side rake angles, cutter geometry, confining pressure, impact frequency, and different lithologies. Torsional impact decreases the force on cutter, and increase the rock breaking efficiency greatly.(4) A3-D simulation with double cutters rock breaking was performed to analyze the variation of cutter space in MSE. By comparing the cutter spacing optimization curve data of the double cutters rock breaking and found that the MSE increases with the cutter spacing decreases in the beginning, and then increases with the cutter spacing increase.In a word, there is an optimal value of the cutter spacing; For the same rock, the optimal cutter spacing under the torsional impact smaller than conventional cutting; The MSE required to cut limestone is much higher than cut sandstone under cutter spacing in any value.(5) Some recommendations to parameter settings of torsional impact drilling assembly and PDC bit cutter were made based on the simulation results.Results of this study can be designed to optimize the PDC bits. |
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