Page 86 - Reservoir Formation Damage

Petrophysics-Flow Functions and Parameters 69

+ 75

.CLEVELAND
.AFTER
PLUGGING
49
30

WOR

15

3O

45
60
II
-75
0.1 O.Z 0.3 0.4 0.5 0.6 0.7 0.6
WATER SATURATION (FRACTION)
Figure 4-1. Effect of pore plugging by clay particles on capillary pressure
(Donaldson, ©1985 SPE; reprinted by permission of the Society of Petroleum
Engineers).

Jerauld and Rathmell (1997) show that the Amott-Harvey wettability index
correlates linearly and increases with the initial saturation for Prudhoe.
Ertekin and Watson (1991) show that the wettability index correlates
linearly and decreases with the average pore-throat length. Figure 4-2 by
Leontaritis et al. (1992) describes the alteration of wettability towards oil-
wet by adsorption of organic matters, such as asphaltenes. Figure 4-3 by
Yan et al. (1997) clearly indicates that the wettability index decreases as
the adsorption of asphaltenes progresses.
Durand and Rosenberg (1998) have determined by cryo-scanning
electron microscopy that the bulk or apparent wettability of clay-bearing
formations is significantly influenced by the type, morphology, quantity,
and location of the clay minerals, and the trapment of fluids in the pore
space. They explain that, when water-wet kaolinite and platy illite are
aged in oil, these minerals absorb some oil components to become oil-
wet. Whereas, the fibrous illite does not show any affinity toward oil and
it remains water-wet. However, even a small amount of kaolinite of platy
illite can make a clay-bearing sandstone oil-wet after aging with oil. Once
transformed into an oil-wet system, as depicted by Durand and Rosenberg