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132 PETROPHYSICS: RESERVOIR ROCK PROPERTIES
Figure 3.24. Log-log plot of RQI versus free fluid index.
where k is the permeability in Darcys, dgr is the diameter of spherical
grains in mm, and ap is the packing constant, which may be estimated
from:
ap = 0.97@-3.3 (3.61)
Substituting Equation 3.61 into Equation 3.60 gives:
k = 10.5 dgr Q3.3 (3.62)
This correlation is valid primarily for sandstone formations.
EFFECT OF WATER SATURATION ON PERMEABILITY
Wyllie and Rose investigated the effect of irreducible water saturation
Swi and porosity on the absolute permeability, and developed the
foilowing empirical correlation 1321 :
2
k=(s) (3.63)
where a, is a constant depending on the hydrocarbon density. For a
medium gravity oil awr = 250 and for dry gas a, = 79, k is in mD, and
@ and S, are fractions [33]. Inasmuch as 2502 e 10~79~, Equation 3.63
indicates that, for the same Cp and Swi, k,, 10 kg, which is not always
