Research progress of laser drilling technology in coal petrography

As an innovative technology with great potential in rock drilling, laser drilling has attracted great attention in research. Laser drilling is a non-contact drilling technology, which has little disturbance and damage to broken and soft formation. Thus, laser drilling can play a significant role in directional drilling of coalbed methane. This paper combs and summarizes the hole forming mechanism and influencing factors of drilling effect of laser drilling in coal petrograph. In the process of laser drilling, the interaction between laser and coal is accompanied by complex physical and chemical effects. It is pointed out that the main hole formation mechanism in coal petrography is laser ablation. The factors influencing the effect of laser drilling on coal petrography are stated from the aspects of laser parameters, rock properties and external environment. The special phenomena and problems of laser drilling on coal petrography are discussed, and comments are stated that the laser ablation involves volatilization, pyrolysis, sublimation, sintering and oxidation of coal components under laser irradiation. To promote the research of laser drilling in coal petrography, it is suggested to strengthen the adaptability study of multi-physical field coupling mechanism, drilling process and drilling device research of laser drilling in coal petrography.