Page 96 - Standard Handbook Petroleum Natural Gas Engineering VOLUME2

$4 Reservoir Engineering

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WATER SATURATION,

INTERMEDIATE - WET
BEREA CORE 2-M016-I

0 20 40 60 BO 100
WATER SATURATION. Y.
Flgure 5-59. Effect of wettability on capillaty pressure [176].

As related by Mungan and Moore [178], three assumptions are made in the
Archie saturation expression (Equation 5-68): all of the brine contributes to
electrical flow: the saturation exponent, n, is constant for a given porous media;
and only one resistivity is measured for a given saturation. Since the saturation
exponent depends on the distribution of the conducting phase, which is depen-
dent on wettability, the foregoing assumptions are valid only for strongly water-
wet conditions. When wettability is altered, the differences in fluid distribution
cause variations in the cross-sectional areas of conductive paths and in the