Environmental Engineering Reference
In-Depth Information
clay mineral
bound
layer
outer
Helmholtz
plane
bound
layer
clay mineral
EXCESS CATIONS
CATION DEFICIENCY
CATION SELECTIVE MEMBRANCE
Figure 3.13
Schematic representation of the formation of a cation-selective membrane in
a constricted pore throat (after Hill et al., 1997)
In preferentially water wet rocks, this is the portion of he pore throats, where
hydrocarbons will reside. If the pore throats are small enough, however:
•
The Helmholtz double layers completely fill the pore throat
•
The pore throat becomes an electrical cation selective mem-
brane (see figure 3.13)
Even if the Helmholtz double layers do not completely fill the pore
throats, capillary forces will restrict the non-wetting fluid from entering
the pore throats.
There is a shear, or slipping plane surface between the Stern and Gouy
layers, which allows movement of the Gouy layer cations without disturb-
ing the Stern layer. The potential difference between this plane and the free
fluid is the Zeta Potential
(Chilingar et al., 1970).
Upon application of DC current, the mobile Gouy layer migrates, in the
direction of the electrical field, toward the negative (cathode) electrode.
This motion of the water molecules and cations within the Gouy layer,
results in the following:
• The motion of the water molecules and cations within the
Gouy layer effectively opens the diameter of the pore throat
to the bound, Stern layer, as shown in figure 3.14.
• Cations, anions, and other fluids in the free fluid will be
dragged through the (now enlarged) pore throat.
•
Both the wetting and non-wetting fluids will be produced.
Extensive experimental work, conducted at The University of Southern
California (Ace, 1955; Amba et al., 1964, 1965; Chilingar et al., 1968,1970,
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