Page 135 - Reservoir Formation Damage

Characterization of Reservoir Rock 117

[OH1 free/moldm' 3

Figure 6-10. Hydroxyl-hematite ion-exchange isotherm indicating the amount
of hydroxyl ion consumed per unit surface area of hematite vs. the hydroxyl
ion concentration in solution (after Tamura et al., 1999; reprinted by permis-
sion of the authors and Academic Press).

The Helmholtz-Smoluchowski equation of the zeta-potential for gran-
ular porous media is given by Johnson (1999) as:

r 4rcuX dU
(6-6)
dp

based on the cylindrical capillary bundle of tubes model. In Eq. 6-6, £
denotes the zeta-potential of the capillary surface, |i is the viscosity, (££ 0)
is the permittivity, (dU I dp) is the streaming potential pressure gradient, U
is the streaming potential, p is pressure, A and L are the cross-sectional area
and length of porous media, respectively, (j) is the porosity, and R is the
electrical resistance. Figures 6-12 and 6-13 by Johnson (1999) show the
dependency of the zeta-potential on the ionic strength and pH of the aqueous
solution, obtained by the electrophoresis and streaming potential methods.

Wettability

Wettability of the pore surface is one of the important factors influenc-
ing the distribution and transport of various fluid phases and therefore
the extent of formation damage in petroleum-bearing formations. Because