Haizeng Pan, Yi Hu, Hejuan Liu, Yintong Guo, Yong Kang, Zhengkuo Ma
Radial horizontal drilling, which utilizes high-pressure water jets for rock breaking, suffers from low efficiency in hard formations, shallow depths, and poor well trajectory control. The laser–water jet combined rock-breaking technology utilizes a high-energy laser to precisely predamage the rock, which is then followed by the water jet to complete hole enlargement and cutting removal. This study investigates the submerged laser–water jet rock-breaking process by analyzing rock samples at different stages, revealing the evolutionary patterns of internal structural characteristics, microscopic properties, and chemical composition. The findings are as follows: the laser phase involves physicochemical changes, while the water jet phase removes damaged rock through impact, cutting, and fatigue effects; the laser-irradiated hole exhibits a conical wedge shape and induces crack propagation, and after water jet erosion, the hole depth changes minimally, but the flaking area expands significantly, confirming effective removal of the laser-damaged zone; the rock surface forms three distinct areas: the irradiation hole, melting zone, and thermal effect zone, with the erosion pit inner wall displaying a dense porous structure where micropores are interconnected by cracks; the proportion of pores with diameters of 0.025–0.1 μm and 0.1–0.16 μm after combined rock breaking is significantly higher than after laser irradiation alone; laser irradiation reduces the contents of plagioclase, calcite, dolomite, and siderite by 8.6%, 5.5%, 0.5%, and 0.8%, respectively, whereas the mineral composition after combined rock breaking closely resembles that of the original rock; elemental analysis shows that laser irradiation decreases the concentrations of C and O while increasing Si, due to the thermal decomposition of carbonate minerals releasing CO 2 . This study provides a theoretical foundation for optimizing combined rock-breaking technology.