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| isbn = 0891816607
| isbn = 0891816607
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''Permeability'' is a property of porous media that characterizes the ease with which fluid can flow through the media in response to an applied pressure gradient. It is a measure of fluid conductivity of porous material. This chapter discusses specific issues relating to the factors influencing the accuracy and precision of permeability determination.
''Permeability'' is a property of porous media that characterizes the ease with which fluid can flow through the media in response to an applied pressure gradient. It is a measure of fluid conductivity of porous material. This article discusses specific issues relating to the factors influencing the accuracy and precision of permeability determination.
==Theoretical background==
==Theoretical background==
* ''L'' = length (cm)
* ''L'' = length (cm)
The units in which permeability is typically expressed are the ''darcy'' (d) and ''millidarcy'' (md). A permeability of 1 d allows the flow of 1 cm<sup>3</sup> per second of fluid with 1 cP (centipoise) viscosity through a cross-sectional area of 1 cm<sup>2</sup> when a pressure gradient of 1 atm/cm is applied. This definition unfortunately contains nonconsistent units, as pressure is expressed in atmospheres rather than in fundamental units. Lowman et al.<ref name=pt05r104>Lowman, S. W., 1972, Definition of selected groundwater terms—revisions and conceptual refinements: U. S. Geological Survey Water Supply Paper 1988, 21 p.</ref>, however, have redefined the darcy unit in the mks system in which square meters represents the standard dimension of permeability. The millidarcy, which is one-thousandth of a darcy, is commonly used in core analysis and oilfield operations.
The units in which permeability is typically expressed are the ''darcy'' (d) and ''millidarcy'' (md). A permeability of 1 d allows the flow of 1 cm<sup>3</sup> per second of fluid with 1 cP (centipoise) viscosity through a cross-sectional area of 1 cm<sup>2</sup> when a pressure gradient of 1 atm/cm is applied. This definition unfortunately contains nonconsistent units, as pressure is expressed in atmospheres rather than in fundamental units. Lowman et al.,<ref name=pt05r104>Lowman, S. W., 1972, Definition of selected groundwater terms—revisions and conceptual refinements: U. S. Geological Survey Water Supply Paper 1988, 21 p.</ref> however, have redefined the darcy unit in the mks system in which square meters represents the standard dimension of permeability. The millidarcy, which is one-thousandth of a darcy, is commonly used in core analysis and oilfield operations.
[[file:permeability_fig2.png|thumb|{{figure number|2}}Relationship among permeability, sorting, and grain size. (From <ref name=pt05r124>Pettijohn, F. J., 1975, Sedimentary rocks, 3rd ed.: New York, Harper and Row, p. 628.</ref>; after Krumbein and Monk, 1942.)]]
[[file:permeability_fig2.png|thumb|{{figure number|2}}Relationship among permeability, sorting, and grain size. (From <ref name=pt05r124>Pettijohn, F. J., 1975, Sedimentary rocks, 3rd ed.: New York, Harper and Row, p. 628.</ref>; after Krumbein and Monk, 1942.)]]