Composite rock-breaking of high-pressure CO2 jet & polycrystalline-diamond-compact (PDC) cutter using a coupled SPH/FEM model

CO 2 drilling is a promising underbalance drilling technology with great advantages, such as lower cutting force, intense cooling and excellent lubrication. However, in the underbalance drilling, the mechanism of the coupling CO 2 jet and polycrystalline-diamond-compact (PDC) cutter are still unclear. Whereby, we established a coupled smoothed particle hydrodynamics/finite element method (SPH/FEM) model to simulate the composite rock-breaking of high-pressure CO 2 jet & PDC cutter. Combined with the experimental research results, the mechanism of composite rock-breaking is studied from the perspectives of rock stress field, cutting force and jet field. The results show that the composite rock-breaking can effectively relieve the influence of vibration and shock on PDC cutter. Meanwhile, the high-pressure CO 2 jet has a positive effect on carrying rock debris, which can effectively reduce the temperature rising and the thermal wear of the PDC cutter. In addition, the effects of CO 2 jet parameters on composite rock-breaking were studied, such as jet impact velocity, nozzle diameter, jet injection angle and impact distance. The studies show that when the impact velocity of the CO 2 jet is greater than 250 m/s, the CO 2 jet could quickly break the rock. It is found that the optimal range of nozzle diameter is 1.5–2.5 mm, the best injection angle of CO 2 jet is 60°, the optimal impact distance is 10 times the nozzle diameter. The above studies could provide theoretical supports and technical guidance for composite rock-breaking, which is useful for the CO 2 underbalance drilling and drill bit design.