Page 360 - Petrophysics

328 PETROPHYSICS: RESERVOIR ROCK PROPERTIES

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
WATER SATURATION

- MERCURY -.+- CORE 1 -** CORE 2
-*- CORE3 * CORE4

Figure 5.13. Oil-water primaly drainage us. mercury, normalized with k/@.

Capillary pressure transposed from mercury data to represent water-
wet, water-oil, or water-air systems (pcWW or p,+) can be obtained from
Equation 5.21. O’Meara et al. showed the close correspondence that can
be obtained between J-function-normalized mercury capillary pressure
curves and curves obtained for water-oil systems using a centrifuge
(Figure 5.13) [ 1 11. The core samples described in Figure 5.13 are cleaned
sandstone cores taken from a one-foot interval.
Inasmuch as it is accepted practice to consider the contact angle for
an air-water system to be equal to zero, one can use this to obtain a
relationship between the contact angle and the saturation of water-oil
systems as follows:

(5.22)

(5.23)

(5.24)
Daw

An airdisplacing water capillary pressure curve is obtained using
Equation 5.22, whereas an oildisplacing water capillary pressure curve