Experimental investigation of hydrophobic and hydrophilic silica nanoparticles on extended surfactant properties: Micro-emulsion, viscosity, and adsorption behaviors

Abstract

The novel applications of nanoparticles and surfactants are of interest for improving chemical oil recovery performance. In this study, two types of hydrophobic and hydrophilic SiO2 nanoparticles (NPs) were used in conjunction with a binary surfactant system (extended Carboxylate and Dioctyl sulfosuccinate (AOT) surfactants at the ratio of 0.6:0.4 by volume). An extensive series of experiments were performed in the presence of API brine containing NaCl: CaCl2 at the 8:2 wt ratio to study microemulsion phase behavior, interfacial tension (IFT), surfactant adsorption onto NP surfaces, solution and microemulsion viscosity, and oil recovery. The results indicate that the microemulsion phase behavior, optimum salinity (S*), and IFT were influenced by the concentrations and surface characteristics of the NPs. Hydrophobic or hydrophilic NPs at 500 ppm in the binary surfactant system could form Type III microemulsion and decrease the S* from 2 to 1.75 wt%. When the NP concentration reached 1000 ppm, the S* reduced to 1.5 wt%. The IFT value of the neat binary surfactant system at the S* was obtained in an ultralow range (0.0013 mN/m), and the IFT value of the hydrophobic NPs exhibited a more significant reduction than the hydrophilic NP systems. The adsorption result demonstrates that Carboxylate surfactant had lower adsorption onto hydrophilic NP than AOT. COSMO σ-profile and screened charge density illustrated that the low coverage of Carboxylate surfactant was from hydrogen bonding interaction, making the surfactant lie flat on the surface. The viscosity of the NP-surfactant solution was affected by the capacity of the surfactant adsorption onto the NP surface. In this regard, adding the hydrophobic NPs at 1000 ppm provided the highest solution viscosity over the entire shear rate and temperature range. The viscosity of the microemulsion formulated by hydrophobic NPs was higher than that of the microemulsion formulated by the hydrophilic NPs. The system with the lower NP concentration had higher microemulsion viscosity than the system with the higher NP concentration. The oil recovery results indicate that the appropriate NP type and concentration in the surfactant system could increase the displacing viscosity and decrease the microemulsion viscosity compared with the neat surfactant flooding system. The success in improving oil recovery was achieved with recovery efficiency of 88% original oil in place (OOIP).