## 1 Introduction  
Colloidal dispersions using liquid suspensions of nanoparticles (NPs) have attracted considerable attention given their potential applications to enhanced oil recovery (EOR) from petroleum reservoirs [1; 2; 3; 4; 5; 6]. NPs penetrate reservoir rocks; the particle diameter is less than 10% of that of the typical pore throat [7; 8]. NPs are adsorbed by oil-water interfaces in rock pores [9; 10; 11; 12; 13]. In addition, mixing NPs with surfactants enhances NP surface activation [14; 15; 16; 17]. For example, electrostatic adsorption of cationic surfactants onto silica NPs renders the particle surface hydrophobic; the silica particles move to the oil phase, further reducing the oil-water interface tension. In principle, adhesion energy is influenced by changes in NP interfacial tension and wettability, as expressed by \(E=\pi R^{2}\gamma_{\text{{\tiny{\tiny{\tiny{\tiny{\tiny{\tiny{\tiny{\tiny{ \tiny{\tiny{\tiny{\tiny{\tiny{\tiny{\tiny{\tiny{\tiny{\tiny{\tiny{\leftleftleftleftleftleftleftleftleft{{ \leftleftleftleftleftleft{{ \leftleftleftleftleftleft{{{ \leftleftleftleftleftleft{{{  {   }}} {{{}_{{}}_{{}_{{}^{{}  
of both reductions in the Debye length and electrostatic attractions between two oppositely charged molecules. If colloidal dispersions precipitate within reservoir rocks, fluidity is compromised because rock permeability decreases [23]. Recently, to increase applications in sandstone reservoirs with high salinity and high temperatures, SiO\({}_{2}\) NPs co-stabilized by a low-molecular-weight ligand (steric stabilization) and a zwitterionic surfactant (electrostatic stabilization) were developed [24]. However, these synthesis techniques are costly and time-consuming, because these methods can obtain only a very small amount of surface-modified NP at once and require many step by step processes. Thus, as the second factor to apply to the reservoir, a more efficient method is required for formation of colloidal dispersion.  
Unlike conventional techniques for synthesis of colloidal dispersions, in this study, we homogeneously mixed anionic polymer with zwitterionic surfactant on the surface of silica nanoparticles in an applied shear stress manner using an ultrasonic homogenizer. Since this method can adsorb polymers and surfactants on the surface of nanoparticles via van der Waals attraction and dipole-charge interaction in a short time, it is very useful and realistic to produce many colloidal dispersions for reservoir applications. More specifically, this study evaluated electrostatic stabilization and particle aggregation at the oil-water interface using surfactants with different electrostatic properties, to enhance colloidal NPs/anionic polymer; of the two surfactants tested, one was cationic [dodecyltrimethylammonium bromide (DTAB)] and the other was zwitterionic (3-(\(N\),\(N\)-dimethylmyristylammoniumio) propanesulfonate, TPS). Then, we also investigated how electrostatic stabilization of NPs affected flow within porous rocks such as core plugging phenomenon. Finally, we explored how the zwitterionic surfactant on NPs dispersions quantitatively affects residual oil saturation according to the capillary number, which is still insufficient in most previous studies. To investigate the effects of changes in residual oil saturation after adsorption of a zwitterionic surfactant, ultimate oil recovery and residual oil saturation were analyzed with and without the zwitterionic surfactant as a function of injected velocity of colloidal dispersions and oil viscosity.