Pore-scale investigation of Al2O3 nanoparticles for improving smart water injection: effect of ion type, ion and nanoparticle concentration, and temperature

Abstract

The central question in this paper asks the synergistic effects of combining Al2O3 nanoparticles (NPs) and smart water at elevated temperatures for enhanced oil recovery (EOR) purposes. For this, different concentrations of NPs were added to the synthetic smart waters and evaluated through visual stability analysis by the addition of two acids (HCl and C2H4O2) and two bases (NH3 and NaOH). They were analyzed by interfacial tension (IFT) measurements at high temperatures. The optimum IFTs were investigated through contact angle, interfacial rheology, and asphaltene adsorption measurements. They were then monitored by absorbance spectroscopy for more stability analysis and injected into a three-layer porous medium for pore-scale crude oil displacement evaluation at high temperatures. PH adjustment results showed an improved nano-smart water stability by HCl at pH < pHIEP. IFT results revealed that oil/water IFT was almost halved by the addition of Al2O3 NPs and ions. Furthermore, in comparison with increasing active ions (Mg2+ and ), reducing inactive ions (Na+ and Cl−) was found to be of greater importance in IFT reduction. A new mechanism for IFT reduction by NPs was also presented based on the interfacial viscosity measurements and asphaltene adsorption analysis. The optimum IFTs also indicated an improved wettability alteration, which was attributed to the expansion of the electrical double layer by potential determining ions (Mg2+) and applied disjoining pressure by Al2O3 NPs. The injection of optimums into the transparent porous medium indicated the highest crude oil recovery of 40% in the secondary injection mode and an incremental crude oil recovery factor of 10% in the tertiary mode. Regarding the water in crude oil emulsions observed during floodings, it was concluded that increasing the number of active ions is of greater significance in emulsification as compared to reducing the inactive ions.