Page 361 - Petrophysics 2E

MEASUREMENT OF CAPILLARY PRESSURE 329

is obtained using Equation 5.23. The ratio of the capillary pressures at
each saturation from S, = 1.0 to S, = Si, is obtained, and the contact
angle for a water-oil system in a porous medium can then be plotted as
a function of the wetting phase saturation. Implicit in Equation 5.24 is
the assumption that the pore size is the same for a given wetting phase
saturation of the two fluids [ 13, 141,

EXAMPLE

The following mercury injection capillary pressure data were obtained
from a sandstone core with k = 26 mD and 4, = 12%. Compute the corre-
sponding water41 capillary pressures for a strongly water-wet system if
the water-oil interfacial tension is 36 mN/m.

Mercury-Air
S(Hg) S(air) P, (Hg-air)
0.05 0.95 4.1
0.40 0.60 8.3
0.50 0.50 34.5
0.55 0.45 82.7
0.60 0.40 144.8
0.65 0.35 220.6

SOLUTION

= (36 x 1.0) x
(480 x 0.766)
= 1.44 x P,(Hg)

Water-Oil
$(oil) S(water) P,(water-oil)
~~~ ~
0.05 0.95 5.9
0.40 0.60 12.0
0.50 0.50 49.7
0.55 0.45 119.2
0.60 0.40 208.7
0.65 0.35 318.0