Coal is typically regarded as a heterogeneous porous medium with discrete pore and fracture structures [171]. Owing to this unique structure, the dynamic migration of CH4 gas during gas injection and displacement in coal can be divided into two distinct components: (1) Free-phase CH4 undergoes seepage through the coal’s fracture network toward the production borehole/well, driven by a pressure gradient. (2) As injected gas increases and CH4 flows out, the CH4 content and concentration within the fractures gradually decrease. Under the CH4 concentration gradient established between the coal matrix blocks and the fractures, adsorbed CH4 within the matrix desorbs and diffuses into the fractures. At the pore-scale level, the migration of CH4 gas molecules within the coal matrix pores during flooding primarily involves desorption and diffusion mechanisms. Scaling up the investigation, the dynamic migration of CH4 gas during gas injection and displacement encompasses multiple transport behaviors—desorption, diffusion, and seepage—occurring within the complex pore–fracture system. Consequently, the dynamic migration behavior of CH4 gas at this scale is fundamentally different from that observed at the microscopic pore level.