Hot dry rock (HDR) is an important renewable energy resource within the overall energy mix. However, its popularization is restricted by drilling costs due to the high hardness and abrasiveness of the rock. As a type of cryogenic fluid, liquid nitrogen (LN2) could aggravate the damage of high-temperature rocks and provide a novel insight in improving the drilling efficiency of HDR. To investigate the rock failure process under the joint action of cutting and jet impingement, a series of experiments were conducted in the present paper. The cutting force was monitored in real-time to evaluate the characteristics of rock-breaking. Then, the 3D topography of cutting grooves was analyzed to determine the rock failure modes (brittle failure or ductile failure). Finally, the rock failure mechanism was investigated by observing micro-structures of cutting grooves including cracks on surfaces and inside the rock. Results indicate that rock strength degrades obviously during the heating process, resulting in a 31.13% decrease in normalized cutting force (F). Meanwhile, the brittle failure of rocks is enhanced at elevated temperatures. This phenomenon can be validated by the fluctuation of cutting force and roughness of cutting grooves. The jet impact can induce thermal stress, thereby, further intensifying the volumetric breakage of rocks. Compared with the water jet, the LN2 shows better performance in improving the rock-breaking efficiency due to its cryogenic feature and lower viscosity. The F reduces by 43.96 and 52.53% with the assistance of water jet and LN2 jet, respectively. Besides, micro-cracks generate with the increasing temperature. The fluid penetrates the rock along these cracks, which rises the width of subsurface cracks and facilitates the subsequent rock cutting.

干热岩 (HDR) 是整体能源结构中的一种重要的可再生能源。但由于岩石硬度高、磨蚀性强，其推广受到钻井成本的制约。作为一种低温流体，液氮 (LN2) 可以加剧高温岩石的破坏，并为提高 HDR 的钻井效率提供新的见解。为了研究切割和射流冲击共同作用下的岩石破坏过程，本文进行了一系列实验。实时监测切削力以评估破岩特性。然后，分析切割槽的 3D 地形以确定岩石破坏模式（脆性破坏或延性破坏）。最后，通过观察切槽的微观结构，包括岩石表面和内部的裂缝，研究岩石破坏机制。结果表明，岩石强度在加热过程中明显下降，导致归一化切削力下降31.13%（F )。同时，岩石的脆性破坏在升高的温度下增强。这种现象可以通过切削力的波动和切削槽的粗糙度来验证。射流冲击会引起热应力，从而进一步加剧岩石的体积破碎。与水射流相比，LN2 由于其低温特性和较低的粘度，在提高破岩效率方面表现出更好的性能。在水射流和LN2射流的帮助下，F分别降低了43.96%和52.53%。此外，随着温度的升高，会产生微裂纹。流体沿着这些裂缝渗入岩石，增加了地下裂缝的宽度并促进了随后的岩石切割。