Synthetic cores containing various percentages of different clay mineralswere flooded with water which contained different types of salts in variedamounts, and the flow rate was measured during the application of directelectrical current at varying current density. Kerosene also was used as theflowing fluid, and some chemical additives, such as sodium acid pyrophosphate, were tested in conjunction with the application of electrical current.
The experimental results indicated that the increase in the flow rate ofliquids was due not only to the electroosmotic effect but also to some changesin the pore structure. These changes in the pore configuration took placeduring the electrochemical treatment and generally resulted in higher finalhydrodynamic permeability. As a result of the physicochemical changes in theclay properties, the tendency of the clay to swell and absorb water wasmarkedly decreased. In these systems, the electrical or electrochemicaltreatment appeared to be an irreversible process. The extent to which theseelectrochemical changes were produced depended in general on the amount ofcurrent passed, the magnitude of potential gradient imposed, the amount andtype of clay minerals present, and the type and concentration of electrolyticsolution used.
The increasing importance of either primary or secondary recovery of oilfrom tight, clayey formations, and the difficulties encountered in suchrecovery due to clay swelling, suggested the possibility of utilizing directelectrical current to augment reservoir energy. The effective permeability tooil, especially around the borehole, greatly affects the productivity of an oilzone. A decrease in the relative oil permeability around the well can be causedby infiltration of the mud cake filtrate. This suggested the use ofelectrochemical treatment as a method for well stimulation.