Research progress and challenges of permeability enhancement technologies for low-permeability coal seams in high-gas mines

Permeability enhancement technology for low-permeability coal seams is a core challenge in the efficient development of coalbed methane, as its mechanistic complexity and engineering adaptability restrict resource conversion efficiency. This study systematically reviews the action mechanisms and applicable boundaries of six technical systems—physical, chemical, gas displacement, thermal, biological, and integrated permeability enhancement—and reveals the synergistic laws and technical bottlenecks of multi-field coupling permeability enhancement. The results show that physical permeability enhancement increases permeability by 3-8 times through mechanical energy or thermal stress, but exhibits poor adaptability to coal seams under high in-situ stress or with high plastic toughness. Chemical permeability enhancement can increase permeability by 1.5-5.0 times via mineral dissolution and interfacial tension regulation, yet carries risks of formation damage and insufficient long-term effectiveness. Gas displacement offers dual benefits of permeability enhancement and carbon sequestration, achieving a permeability increase of 2 to 6 times, but CO₂ adsorption-induced swelling leads to a short-term permeability reduction of 20% to 40%. Thermal permeability enhancement improves permeability by 2 to 8 times through thermal cracking and phase change effects, although high energy consumption restricts its economic feasibility. Biological permeability enhancement is environmentally friendly but limited by coal rank. Integrated permeability enhancement achieves a nonlinear improvement in permeability through multi-mechanism synergy, while facing challenges of process complexity and cost accumulation. Current technologies are constrained by unclear multi-field coupling mechanisms, poor adaptability to deep conditions, and insufficient long-term stability. Future development trends should focus on interdisciplinary innovation. This review provides a theoretical basis and technical pathway for the safe and efficient development of low-permeability coalbed methane, supporting the upgrading of the unconventional natural gas industry under the "dual carbon" goals.