in fluid mechanics
and the earth sciences
(commonly symbolized as κ
, or k
) is a measure of the ability of a porous material
(often, a rock
or unconsolidated material) to allow fluids to pass through it.
unit for permeability is m<sup>2</sup>. A traditional unit for permeability is the darcy
(D), or more commonly the millidarcy
(mD) (1 darcy <math>approx</math>10<sup>−12</sup>m<sup>2</sup>). The unit of cm<sup>2</sup> is also sometimes used (1 m<sup>2</sup> = 10<sup>4</sup> cm<sup>2</sup>).
The concept of permeability is of importance in determining the flow characteristics of hydrocarbons
reservoirs, and of groundwater
For a rock to be considered as an exploitable hydrocarbon reservoir without stimulation, its permeability must be greater than approximately 100 mD (depending on the nature of the hydrocarbon - gas reservoirs with lower permeabilities are still exploitable because of the lower viscosity
of gas with respect to oil). Rocks with permeabilities significantly lower than 100 mD can form efficient seals
(see petroleum geology
). Unconsolidated sands may have permeabilities of over 5000 mD.
The concept has also many practical applications outside of geology, for example in chemical engineering
Permeability is part of the... Read More