Page 365 - Petrophysics 2E

CENTRIFUGE MEASUREMENT OF CAPILLARY PRESSURE 333

I
I

0 L
A
I I
I
I
s y i L

B
0
0
Figure 5.17. Centrifugal determination of capilla y pressure showing the variation
ofpressure and water saturation as a function of length of the core.

CALCULATION OF CENTRIFUGE CAPILLARY PRESSURE DATA

Slobod and Blum and Slobod et al. developed a method for computing
the capillary pressure at the top of the core [14, 151. The equation for
capillary pressure in a centrifugal force field is derived beginning with
Equation 5.9, which was obtained for capillary rise in a straight tube. The
centrifugal acceleration, a, is:

a=- ve' (5.25)
r
2rN
ve = - (5.26)
60

where Ve is the rotational velocity, cds. Dividing a by gc to obtain the
ratio of centrifugal acceleration to the gravitational acceleration, then
substituting a/& for gc in Equation 5.14:

a - 4n2rN2
-
-
gc 981 x 3600