• Liquid nitrogen immersion (LNI) enhances coal seam permeability by inducing thermal stress and moisture phase transformation, which damage pore structures and promote fracture expansion.
• NMR and nitrogen adsorption experiments show that LNI increases the T2 peak area and BJH total pore volume (to 14.99 mm³/g) while reducing BET surface area to 6.02 m²/g, indicating pore structure optimization.
• Fractal dimension analysis reveals enhanced pore complexity and connectivity after LNI, with D1 increasing from 2.804 to 2.837 and D2 decreasing from 2.757 to 2.594.
• Multiple LNI cycles significantly improve micropore structure and connectivity, offering a promising method for enhancing coalbed methane extraction efficiency.