*2.3.2 Water imbibition: tight reservoirs*

As in oil shales, water imbibition can be employed to enhanced oil and gas recovery in tight reservoirs [90]. Oil is preferentially driven out from pores during water imbibition due to greater capillary forces. Surfactants may be introduced during water imbibition to convert the wettability of rock from *oil-wet* to *water-wet* and to reduce the interfacial tension between liquid phases—oil and water—in the reservoir.

### *2.3.3 Application of electrokinetics potential*

Electrokinetic potential instigates colloidal dispersion. This technique enhances the effect of water imbibition in clay-rich and tight reservoirs (e.g., sandstone) by stimulating colloidal movement through the dislodgement and transport of pore clay linings [89]. The removal of clay linings in pores enlarges pore throats and/or creates new flow pathways, causing a direct increase in permeability and porosity. Electrokinetic potential and water injection can be used in tandem to improve efficiency.
