Traditional categorization of gas flow regimes in porous media relies phenomenally on Darcy's law, yielding phenomenologically a “pre-Darcy” flow regime and a “post-Darcy” flow regime before and after the linear region, respectively. This study redefines the classification of gas flow regimes by integrating the underlying flow mechanisms, proposing four distinct regimes: the slip regime, the Darcy regime, the inertia regime, and the turbulence regime. Through a scaling analysis of the Forchheimer equation, a dimensionless number, Rd, is introduced as a criterion for the onset of the inertia regime. The classification is validated using an independently established gas seepage experimental platform, which confirms the presence of gas slip effects in the “pre-Darcy” regime. Experimental data from the inertia regime show a linear increase of critical Rd with a rising permeability (${\text{Rd}}_{\mathrm{critical}}\propto k$). The deduced critical Reynolds number, Re, further substantiates that at low permeability, gas slip effects delay the transition to the inertia regime, while at high permeability, increased pore size or decreased tortuosity may hinder the generation of inertial backflow. Furthermore, the Forchheimer equation provides a more accurate description of both the Darcy and inertia regimes compared to the cubic law, with its inertial coefficient determined through appropriate fitting correlations. This study offers valuable insights into gas flow regimes within porous media, and it provides experimental results for further reference.

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• Flows in porous media
• Geophysical fluid dynamics
• Laminar flows
• Low Reynolds number flows
• Microfluidics
• Rarefied flows