Page 85 - Standard Handbook Petroleum Natural Gas Engineering VOLUME2

Basic Principles, Definitions, and Data 73

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RECIPROCAL MEAN PRESSURE, (atrn)"
Figure 5-50. Gas slippage in core [128].
shows the variation in permeability as a function of mean pressure for hydrogen,
nitrogen, and carbon dioxide. Klinkenberg found that by extrapolating all data
to infinite mean pressure, the points converged at an equivalent liquid per-
meability (kJ, which was the same as the permeability of the porous medium
to a nonreactive single-phase liquid. From plots of this type, Klinkenberg showed
that the equivalent liquid permeability could be obtained from the slope of the
data, m, the measured gas permeability, kg, at a mean flowing pressure ji, at
which k, was observed
k m
k, = (5-77)
l+&) = kc-=
P
where b is a constant for a given gas in a given medium and is equal to m
divided by kp. The amount of correction, known as the Klinkenberg effect, varies
with permeability and is more significant in low permeability formations.
In recent studies [ 129,1301 with very low permeability sandstones, liquid
permeabilities were found to be less than gas permeabilities at infinite mean
pressure, which is in contrast with the prior results of Klinkenberg. Furthermore,
it has been shown [ 1301 that liquid permeabilities decreased with increasing
polarity of the liquid, For gas flow or brine flow in low-permeability sandstones,
permeabilities were independent of temperature at all levels of confining
pressure [130]. The data [l30] showed that for a given permeability core sample
at a given confining pressure, the Klinkenberg slip factors and slopes of the