CO₂ 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 CO₂ 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 CO₂ 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 CO₂ 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 CO₂ 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 CO₂ jet is greater than 250 m/s, the CO₂ 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 CO₂ 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 CO₂ underbalance drilling and drill bit design.

CO ₂钻井是一种很有前途的欠平衡钻井技术，具有切削力小、冷却强、润滑性好等优点。然而，在欠平衡钻井中，CO ₂射流与多晶金刚石复合片（PDC）刀具耦合的机理尚不清楚。据此，我们建立了耦合光滑粒子流体动力学/有限元法（SPH/FEM）模型来模拟高压CO _{2的复合破岩。}喷射和 PDC 切割机。结合实验研究结果，从岩石应力场、切削力和射流场等角度研究了复合材料破岩机理。结果表明，复合破岩能有效缓解振动和冲击对PDC刀具的影响。同时，高压CO ₂射流对携带岩屑有积极作用，可有效降低PDC刀具的温升和热磨损。此外，还研究了CO ₂射流参数对复合材料破岩的影响，如射流冲击速度、喷嘴直径、射流喷射角度和冲击距离。研究表明，当 CO ₂射流的冲击速度大于 250 m/s 时，CO₂喷气机可以迅速打破岩石。发现喷嘴直径的最佳范围为1.5~2.5 mm，CO ₂射流的最佳喷射角度为60°，最佳冲击距离为喷嘴直径的10倍。上述研究可为复合材料破岩提供理论支撑和技术指导，对CO ₂欠平衡钻井和钻头设计具有参考价值。