Theoretical and Simulation Study of CO2 Laser Pulse Coupled with Composite Mechanical Drill Bit for Rock-Breaking Technology

Facing challenges of low efficiency and severe wear in deep hard formations with conventional drilling bits, this study investigates the synergistic rock-breaking technology combining a pulsed CO2 laser with mechanical bits. The background highlights the need for novel methods to enhance drilling speed in high-strength, abrasive strata where traditional bits struggle. The theoretical analysis explores the thermo-mechanical coupling mechanism, where pulsed laser irradiation rapidly heats the rock surface, inducing thermal stress cracks, micro-spallation, and strength reduction through mechanisms like mineral thermal expansion mismatch and pore fluid vaporization. This pre-damage layer facilitates subsequent mechanical fragmentation. The research employs finite element numerical simulations (using COMSOL Multiphysics with an HJC constitutive model and damage evolution criteria) to model the coupled laser–mechanical–rock interaction, capturing temperature fields, stress distribution, crack propagation, and assessing efficiency. The results demonstrate that laser pre-conditioning significantly achieves 90–120% higher penetration rates compared to mechanical-only drilling. The dominant spallation mechanism proves energy-efficient. Conclusions affirm the feasibility and significant potential of CO2 laser-assisted drilling for deep formations, contingent on optimized laser parameters, composite bit design (incorporating laser transmission, multi-head layout, and environmental protection), and addressing challenges, like high in-situ stress and drilling fluid interference through techniques like gas drilling. Future work should focus on high-power laser downhole transmission, adaptive control, and rigorous field validation.