A several-fold increase in the flow rate of liquids in synthetic and natural sandstone cores was observed upon application of direct electrical current. These results present the possibility of using direct electric treatment to stimulate wells or enhance water injectivity.
Electroosmosis has long been applied in soil engineering, and there are several patents granted on the removal of water from clayey and silty soils by electroosmosis. These techniques have been used successfully in Germany, England, the U.S.S.R. and Canada in drying water-logged soils for heavy construction. Casagrande documented a good example of electroosmosis in a large-scale soil drying operation in Salzgitter, Germany, during the construction of a double-track railway cutting in a loose loam deposit. Well electrodes were 7.5 m deep and 10 m apart. Before the application of electrical potential, the water flow rate was 0.4 cu m/day/20 wells. potential, the water flow rate was 0.4 cu m/day/20 wells. An electrical potential of 180 v and 19 amps/well increased the flow rate to 60 cu m/day/20 wells, or 150 times the original rate.
We and our colleagues have conducted extensive research on the effect of direct electrical current on permeability of sandstone cores. In some of these permeability of sandstone cores. In some of these earlier experiments the flow rate of water was increased by as much as 32-fold on application of direct electrical current, whereas in other cases the increase in flow rate was only about twofold. It was not clear as to why the volumetric rate of flow increased much more in some cases than in others. It was concluded that there is a possibility of using direct electrical current to enhance the injectivity of water in waterflood systems, or simply to increase the rate of production in tight formations. Amba et al. have discussed production in tight formations. Amba et al. have discussed the economics.
Amba et al. reported a 175 percent increase in flow rate at 1.5 psi pressure drop upon application of a potential gradient of 4.5 v/cm and a current density of 0.28 milliamp/sq cm. Chilingar et al. reported a 33.7-fold increase in water flow rate at 3.0 psi pressure drop upon application of a potential gradient pressure drop upon application of a potential gradient of 7.5 v/cm and a current density to 20 milliamp/sq cm.
Adding CaCl2 (0.1 to 0.5 percent by weight) to the flowing liquid increased the electrosmotic flow rate and resulted in electrochemical changes in the porous medium. These changes were evidenced by porous medium. These changes were evidenced by the higher final permeability upon discontinuation of the treatment (hysteresis effect). Chilingar et al. discovered, however, that the volumetric rate of flow increased to a lesser degree on using concentrated formation brines.
Tikhomolova studied the displacement of immiscible liquids in a porous medium. She compared the effectiveness of displacement caused by capillary forces only (imbibition) with that of displacement owing to application of an electric field to the system (electroosmotic displacement) in relation to the capillary radii of powder systems. Based on her experiments, electroosmosis substantially increases the rate of displacement of nonpolar kerosene over the entire range of particle sizes studied (16 to 20, 12 to 16, 8 to 12, and 4 to 8 microns). The influence of electroosmosis increases with decrease in size of silica particles and with increase in backpressure applied to the system.