Application of Electrokinetics for Enhanced Oil Recovery - Electrokinetics for Petroleum and Environmental Engineers - page 115

E

P

Figure 3.6 Schematic representation of figure 3.5. Rock/soil polarized by an electric field,
E (after Hill, 1999).

3.7 Electro-chemical Basis for DCEOR

When electrical current is passed between electrodes embedded in the
earth, several phenomena can, and usually do, occur. The best way to
treat this situation is via the concept of coupled flows, introduced by Lars
Onsager (1931a, 1931b), for which he received the 1968 Nobel Prize in
chemistry (Onsager, 1969).

3.7.1 Coupled Flows and Onsager's Principle

Five mechanisms appear to be operative, in DCEOR, based on available
field and laboratory data:

• Joule heating
• Electromigration
• Electrophoresis
• Electroosmosis
• Electrochemically enhanced reactions

These mechanisms are often collectively called electrokinetics . Figure 3.7
is a qualitative representation of the relative energy requirements for these
mechanisms (with the middle three merged as “electrokinetic mass trans-
port”), as well as that required for electrically fusing (melting) the rock.