Previous studies have clarified microscale CH4 transport mechanisms during gas injection displacement and revealed molecular-level migration-production dynamics. However, at the macroscale, the dynamic transport behavior of CH4 remains unexplored, and it is unknown whether macroscale manifestations align with microscale properties. Furthermore, existing theoretical models oversimplify diffusion processes by substituting the CH4 diffusion coefficient with values measured under single-gas conditions—an approach lacking physical justification. Critical knowledge gaps persist regarding the applicability of unary gas diffusion models to CH4’s dynamic diffusion behavior during displacement, and the fundamental discrepancies between displacement-driven diffusion dynamics and single-gas diffusion characteristics demand rigorous investigation.