# Dictionary Definition

pervious adj : admitting of passage or entrance;
"pervious soil"; "a metal pervious to heat" [ant: impervious]

# User Contributed Dictionary

## English

### Pronunciation

- Rhymes: -ɜː(r)viəs

### Adjective

- (of a rock type) allowing water to pass through via its joints.
- accepting of new ideas

# Extensive Definition

Permeability in the earth
sciences (commonly symbolized as κ, or k) is a measure of the
ability of a material (typically, a rock or
unconsolidated material) to transmit fluids. It is of great
importance in determining the flow characteristics of hydrocarbons in oil and gas reservoirs, and of groundwater in aquifers. It is typically
measured through calculation of Darcy's law.

## Formula

The intrinsic permeability of any porous material is:- _=C \cdot d^2

- _ is the intrinsic permeability [L2]
- C is a dimensionless constant that is related to the configuration of the flow-paths
- d is the average, or effective pore diameter [L]

Permeability needs to be measured, either
directly (using Darcy's law)
or through estimation
using empirically
derived formulas.

A common unit for permeability is the darcy (D), or more commonly the
millidarcy (mD) (1 darcy \approx10−12m2). Other units are
cm2 and the
SI m2.

Permeability is part of the proportionality
constant in Darcy's law
which relates discharge (flow rate) and fluid physical properties
(e.g. viscosity), to a
pressure gradient applied to the porous media. The proportionality
constant specifically for the flow of water through a porous media
is the hydraulic
conductivity; permeability is a portion of this, and is a
property of the porous media only, not the fluid. In naturally
occurring materials, it ranges over many orders of magnitude (see
table below for an example of this range).

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.

## Tensor permeability

To model permeability in anisotropic media, a
permeability tensor is
needed. Pressure can be applied in three directions, and for each
direction, permeability can be measured (via Darcy's law
in 3D) in three directions, thus leading to a 3 by 3 tensor. The
tensor is realized using a 3 by 3 matrix
being both symmetric
and positive
definite (SPD matrix):

- The tensor is symmetric by the Onsager reciprocal relations.
- The tensor is positive definite as the component of the flow parallel to the pressure drop is always in the same direction as the pressure drop.

The permeability tensor is always diagonalizable (being
both symmetric and positive definite). The eigenvectors will yield the
principal directions of flow, meaning the directions where flow is
parallel to the pressure drop, and the eigenvalues representing the
magnitude of flow along principal directions.

## Ranges of common intrinsic permeabilities

These values do not depend on the fluid properties; see the table derived from the same source for values of hydraulic conductivity, which are specific to the material through which the fluid is flowing. Source: modified from Bear, 1972## See also

## Footnotes

## References

- Bear, Jacob, 1972. Dynamics of Fluids in Porous Media, Dover. — ISBN 0-486-65675-6

- Wang, H. F., 2000. Theory of Linear Poroelasticity with Applications to Geomechanics and Hydrogeology, Princeton University Press. ISBN 0691037469

## External links

pervious in German: Permeabilität
(Petrophysik)

pervious in Spanish: Permeabilidad

pervious in French: Perméabilité (fluide)

pervious in Italian: Permeabilità

pervious in Dutch: Permeabiliteit
(geologie)

pervious in Japanese: 透水性

pervious in Norwegian: Permeabilitet
(geologi)

pervious in Polish: Przepuszczalność
hydrauliczna

pervious in Portuguese: Permeabilidade
(geologia)

# Synonyms, Antonyms and Related Words

accessible, amenable, approachable, attainable, available, come-at-able,
excretory, exudative, findable, getatable, gettable, impressionable, influenceable, leaky, malleable, movable, obtainable, oozy, open, open to, open-minded,
openable, penetrable, percolative, permeable, persuadable, persuasible, plastic, pliable, pliant, porose, porous, procurable, reachable, receptive, responsive, runny, securable, suasible, suggestible, susceptible, swayable, to be had, transudative, weak, weepy, within reach