|Publisher||American Petroleum Institute||Language||English|
|Content Type||Conference Paper|
|Title||The Permeability Of Porous Media To Liquids And Gases|
|Authors||L. J. Klinkenberg, Shell Development Co|
|Source||Drilling and Production Practice, 1941|
|Copyright||1941. American Petroleum Institute|
The standard procedure for determining the permeability of porous media according to APZ Code No. 27 (first edition, October 1935) is based on the fundamental assumption that, as long as the rate of flow is proportional to the pressure gradient, the permeability constant of a porous medium is a property of the medium, and is independent of the fluid used in its determination. Although this is true for most liquids, the permeability constant as determined with gases is dependent upon the nature of the gas, and is approximately a linear function of the reciprocal mean pressure. This effect can be explained by taking into account the phenomena of slip, which are related closely to the mean free paths of the gas molecules. The apparent permeability extrapolated to infinite pressure gives a permeability constant which is a characteristic of the porous medium only.
It has become common practice in the oil industry to determine the permeability of core material with dry air; the equipment usually employed for this determination is arranged to operate with the outlet of the sample at or near atmospheric pressure.1a This practice is based on the fundamental assumption that, as long as Darcy's law is obeyed, i.e., as long as the rate of flow is proportional to the pressure gradient,? the permeability constant of a porous medium is a property of the medium, and is independent of the fluid used in its determination.8 Therefore, the results obtained by laboratory measurements with air are taken to be applicable to the homogeneous flow of either oil or gas in underground reservoirs. The fundamental assumption that the permeability of a porous medium is independent of the fluid used in its determination is illustrated by Muskat4 with a few measurements of highly permeable sandstones to air and liquid. However, Muskat5 gives a table of results of measurements on the permeability to water and air of a number of oil sands, carried out by Fancher, Lewis, and Barnes,6 showing large discrepancies between the permeability to air and water-most values found for water being lower than for air. Many cases of such discrepancies between the permeabilities to air and those to water and other liquids also were observed during investigations carried out in the laboratories of the Bataafsche Petroleum Maatschappij, Amsterdam, The Netherlands, and of the Shell Development Company, Emeryville, Calif. In general it was found that, with highly permeable media, the differences between liquid and air permeabilities were small, whereas these differences were considerable for media of low permeability. These discrepancies made it desirable to, investigate the validity of the assumption that the permeability of a porous medium is independent of the nature of the fluid with which the determination is carried out. The investigation has shown that the permeability to a gas is a function of the mean free path of the gas molecules, and thus depends on factors which influence the mean free path, such as the pressure, temperature, and the nature of the gas.
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