Thermal Damage Mechanism and Micro-mechanical Property Analysis of Carbonate Rocks Under Laser Irradiation

Extracting oil and gas from deep and ultra-deep levels poses significant technical and financial challenges, prompting the exploration of innovative rock-breaking techniques due to the wear and efficiency issues of traditional rotary drilling methods. Laser technology offers a non-contact method for breaking rock, and it remains largely unaffected by the high temperatures and pressures in deep and ultra-deep wells. In this study, the effects of laser irradiation on carbonate rocks are analyzed from two perspectives: irradiation temperature and rock damage. Besides, nanoindentation technology is used to assess the micro-mechanical properties of the irradiated limestone. The temperature at the irradiation center of the specimen surface decreases with longer irradiation time. It is positively correlated with laser power but first increases and then decreases with the laser irradiation distance. The optimum damage to the specimens appears at a laser power of 148 W, an irradiation time of 150 s and a laser irradiation distance of 2 mm. The original rock hardness of 2.35 GPa decreases to 1.41 GPa after laser irradiation, a reduction of 40%. Similarly, the elastic modulus drops from 58.99 GPa to 36.14 GPa, reflecting a 38.74% decrease. In addition, the surface morphological features of the specimens are divided into three zones: the ablation zone, the thermal metamorphic zone, and the thermally affected zone. Laser irradiation of limestone leads to the greatest mass loss at temperatures between 600 °C and 890 °C. The calcite minerals in the thermally metamorphosed zone have decreased by 59.7%. The experimental results offer valuable guidance and data support for the application and modeling of laser rock-breaking techniques.