Investigation of the effect of engineered water/nanofluid hybrid injection on enhanced oil recovery mechanisms in carbonate reservoirs

Changing the salinity and ionic composition of the injected water and designing “engineered water” (EW) is an enhanced oil recovery approach which affects the wettability of carbonate reservoirs and improves the oil recovery in many cases. Application of nanoparticles also affects oil production by various mechanisms such as altering the wettability, changing the viscosity of the oil and the injected fluid, and changing the interfacial tension. The benefits of combining these two approaches and developing a hybrid method are investigated in this paper. Experiments and measurements of different characteristics such as contact angle, zeta potential, particle size, ATR (attenuated total reflectance) analysis, ESEM (environmental scanning electron microscope) imaging, ion/nanoparticle deposition, and microemulsion formation were completed to analyze the influence of the hybrid method on rock/oil/brine interactions. Core flooding tests were also conducted to study the performance of the method to improve oil recovery. The most effective EW was selected by adjusting the concentrations of magnesium, calcium, and sulfate ions of Persian Gulf water. Nanoparticles such as SiO2, CaCO3, TiO2, and gamma Al2O3 were also studied to achieve the longest stability. Finally, the effect of combining the optimum states of engineered brine and nanoparticles on different mechanisms was investigated. Our results showed that spiking the injection brine with sulfate ions and using a hybrid method with silica nanoparticles at a concentration of 0.1 wt% provided the best effect on the enhanced oil recovery. This combination altered the wettability more than standalone methods. Also, there was a decrease in adsorption of nanoparticles on the rock surface, which controls the retention mechanism. Therefore, the presence of more nanoparticles in the fluid flow leads to the formation of microemulsions and increases in the viscosity of the injected fluid, which affects the sweep efficiency in porous media.