Page 88 - Reservoir Formation Damage

Petrophysics-Flow Functions and Parameters 71

(1998) schematically in Figure 4-4b, clay-bearing sandstone retains oil
due to large capillary forces and becomes water repellent. They deter-
mined that, when aged with water, the fibrous illite in an oil-saturated
formation transforms to become water-wet. Therefore, they have con-
cluded that adsorption and capillary forces act together to transform a
clay-bearing formation from water-wet to oil-wet or vice-versa, depending

Water wet clay
^
Oil

Sandstone grain Sandstone grain Sandstone grain
Water wet Water wet il retained
clay clay by capillarity
becoming
Oil globules oil wet
(b)

(c)
Continuous
Discontinuous pathways
pathway
Figure 4-4. Schematic description of the wettability effect at different scales:
a) between clay particles, b) at microscopic scale between sandstone grains,
and c) at bulk porous formation scale (Reprinted from Journal of Petroleum
Sc/ence and Engineering, Vol. 19, Durand, C., and Rosenberg, E., "Fluid
Distribution in Kaolinite- or Illite-Bearing Cores: Cryo-SEM Observation Versus
Bulk Measurements," pp. 65-72, ©1998, with permission from Elsevier
Science).