Numerical simulation of thermal effects of laser irradiation on coal and rock

To study the thermal effect of laser on coal and rock will benefit to understand the hole-forming mechanism of laser acting on coal and rock, so as to provide theoretical basis for the application of laser in CBM horizontal drilling. Based on heat transfer theory, the mathematical model of laser drilling of coal and rock by uniform light beam was established to simulate the transient temperature distribution in rocks exposed to a laser beam by COMSOL Multiphysics software. The influences of laser power, laser spot radius and irradiation time on the thermal effects were analyzed. The evaporation of coal rock at high temperature was numerically simulated, and the hole shape formed after gasification was obtained. The simulation results show that the main factors affecting the drilling depth are the laser power and radiation time, and the main factor affecting the diameter of the hole is the spot diameter. The main thermal effect of laser interaction with coal and rock is laser ablation. Once the laser is applied for methane directional well, it will decrease dramatically the solid debris, thus reducing the difficulty of debris removal during drilling.