This book provides a comprehensive investigation into the multi-scale dynamic migration characteristics of CH4 in coal during gas injection displacement, with a focus on the following key aspects:  Pore-scale dynamic migration behavior of CH4 molecules during gas injection displacement. LBM simulation of dynamic CH4 migration in coal under gas injection conditions. Experimental analysis of CH4 migration in coal particles during displacement. Engineering applications and displacement performance prediction for underground N- injection in coal seams. This study has attracted engineers and scientists across multiple fields including mining, safety, materials, civil, and geological engineering. Designed for undergraduate and graduate students interested in gas injection displacement, researchers focused on microscopic displacement efficiency, and engineers in the energy industry or specialized wellbore design, this book serves as an essential reference for advancing both theory and practice in enhanced coalbed methane recovery.