Page 385 - Petrophysics 2E

CAPILLARY NUMBER 353

1-l
0.9 -

E OB-
w
4: 0.7-
~ ~ ~ ~ ~ ~ E ~ ~ ~ - ~ ~ ~ ~ ~ ~ ~ "
w 0.6-
6
LL
W 0.5 -
5 AVERAOE PORE srE - ------&'
W
3 0.4- WlDEPORESlZE
w
0
4 0.3-
a
v,
0 0.2-
0.1 -
01 I ,,,,,,,, r ,1111.1 I l,,,,, I I ,,,,,,,, , I,,,,,,, 1 ,,,,,,,
1E-07 1E-06 1E05 1E-04 1E.03 1EM 1E-01

The capillary number for field waterfloods ranges from to lo-*.
Laboratory studies have shown that the value of the capillary number
can have a marked influence on the ultimate recovery of oil. In order
to study the effects of n, on oil recovery, Melrose and Bradner defined
the microscopic displacement efficiency as the ratio of the mobile oil
saturation to the total oil saturation (321:

(5.68)

As the value of n, is increased to 1 0-4, there is no noticeable effect on
the displacement efficiency (the residual oil saturation for a given system
remains constant). At values greater than however, a significant
increase of displacement efficiency is observed. At values greater
than ED becomes 1.0 and complete displacement of oil occurs
(Figure 5.23). Therefore, the critical value of n, has been established to
be equal to At values of n, less than the capillary forces are
dominant and the oil displacement occurs by movement of oil ganglia
several pore diameters in length. The residual oil saturation is distributed
as isolated droplets and groups (depending on the wetting properties).
When n, exceeds the viscous displacement forces dominate and
begin to increase the displacement efficiency.