Permeability To Gases
Sometimes permeability to gases can be somewhat different that those for liquids in the same media. One difference is attributable to "slippage" of gas at the interface with the solid when the gas mean free path is comparable to the pore size (about 0.01 to 0.1 μm at standard temperature and pressure). See also Knudsen diffusion and constrictivity. For example, measurement of permeability through sandstones and shales yielded values from 9.0x10−19 m2 to 2.4x10−12 m2 for water and between 1.7x10−17 m2 to 2.6x10−12 m2 for nitrogen gas. Gas permeability of reservoir rock and source rock is important in petroleum engineering, when considering the optimal extraction of shale gas, tight gas, or coalbed methane.
Read more about this topic: Permeability (earth Sciences)
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—Ralph Waldo Emerson (1803–1882)