Permeability of porous media: Role of the critical pore size

The knowledge of the permeability of porous media is crucial to understand fluid flow in various natural and artificial materials. Due to the complex nature of pore structure, the pore characteristic (porosity and pore radius) determining the permeability has long been under discussion. Here we determined the critical pore radius, which is the radius of the largest sphere that can freely pass through a porous medium, using the water expulsion method, an experimental technique measuring the pressure at which gas passes through a water-saturated porous medium. We demonstrate that the critical pore radius correlates well with the permeability for a variety of porous granular media and volcanic products with an extensive range of porosities (0.71%-50%) and permeabilities (10(-20)-10(-10)m(2)). We also obtained a porosity-critical pore radius-permeability relationship that provides a better prediction of the permeability compared with predictions obtained by previous correlations.