Application of Electrokinetics for Enhanced Oil Recovery - Electrokinetics for Petroleum and Environmental Engineers - page 118

temperature and lowers the viscosity of the crude, making it easier to pro-
duce. As shown in figure 3.7, Joule Heating requires the largest energy dis-
sipations and consequently the greatest potential (voltage) gradients of the
5 DCEOR mechanisms.

3.7.3 Electromigration

Movement of dissolved ionic components, such as (positively charged)
cations and (negatively charged) anions under the influence of an applied
electric field. Electromigration forms the basis of electro-refining and elec-
tro-plating metallurgical processes, where metallic cations migrate from
anode to cathode. Asphaltenes, which are negatively charged, will migrate
toward the anode.

3.7.4 Electrophoresis

Charged colloidal particles, suspended in solution, will also migrate under
the influence of an electrical field, similar to electromigration. In as much as
clays are generally negatively charged, they will move away from the cath-
ode and toward the anode. This process may clear blocked pore-throats and
improve permeability, resulting in increased oil production (Tchillingarian,
1952) or be used to transport organisms and nutrients (Chilingar et al., 1997).

3.7.5 Electroosmosis

Helmholtz double layers formed in the connate waters adjacent to clay
minerals form cation selective membranes in narrow pore throats, allow-
ing hydrated cations and water molecules to pass through the pore throats,
but blocking hydrated anions. The membrane, in this case, is not a physical
membrane as it is in membrane filters, but an electrochemical one. This
mechanism has been utilized to dewater expansive clays, and increase
apparent reservoir permeability, resulting in increased oil production.
This is essentially the definition of electroosmosis used by Leo Casagrande
(1952, 1959), as well as that used by Gray and Mitchell (1967), Mitchell
(1993), and Tikhomolova (1993).

3.7.6 Electrochemically Enhanced Reactions

Reactions between the pore fluids and matrix materials enhanced by
Eh/pH changes brought about by the passage of electrical current.
Electrochemically enhanced reactions appear to enhance the breakdown