Changes

==Theoretical background==

==Theoretical background==

[[file:permeability_fig1.png|left|thumb|{{figure number|1}}Modified schematic diagram of Darcy's experimental apparatus. (Modified from <ref name=pt05r56>Folk, R. L., 1959, [http://archives.datapages.com/data/bulletns/1957-60/data/pg/0043/0001/0000/0001.htm Practical petrographic classification of limestones]: AAPG Bulletin, v. 43, p. 1–38.</ref>.)]]

[[file:permeability_fig1.png|300px|thumb|{{figure number|1}}Modified schematic diagram of Darcy's experimental apparatus. (Modified from <ref name=pt05r56>Folk, R. L., 1959, [http://archives.datapages.com/data/bulletns/1957-60/data/pg/0043/0001/0000/0001.htm Practical petrographic classification of limestones]: AAPG Bulletin, v. 43, p. 1–38.</ref>.)]]

The fundamental relationship given by Henry<ref name=pt05r44>Darcy, H., 1856, Les Fontaines Publiques de la Ville de Dijon: Paris, Victor Dalmont, p. 590–594.</ref> is the basis for permeability determination. Darcy's law originates from the interpretation of the results of the flow of water through an experimental apparatus, shown in [[:file:permeability_fig1.png|Figure 1]]. In this experiment, water was allowed to flow downward through the sand pack contained in an iron cylinder. Manometers located at the input and output ends measured fluid pressures, which were then related to flow rates to obtain the following fundamental Darcy's law:

The fundamental relationship given by Henry<ref name=pt05r44>Darcy, H., 1856, Les Fontaines Publiques de la Ville de Dijon: Paris, Victor Dalmont, p. 590–594.</ref> is the basis for permeability determination. Darcy's law originates from the interpretation of the results of the flow of water through an experimental apparatus, shown in [[:file:permeability_fig1.png|Figure 1]]. In this experiment, water was allowed to flow downward through the sand pack contained in an iron cylinder. Manometers located at the input and output ends measured fluid pressures, which were then related to flow rates to obtain the following fundamental Darcy's law:

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 cm³ per second of fluid with 1 cP (centipoise) viscosity through a cross-sectional area of 1 cm² 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 cm³ per second of fluid with 1 cP (centipoise) viscosity through a cross-sectional area of 1 cm² 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.

==Factors controlling permeability==

==Factors controlling permeability==