Improved Oil Recovery in Carbonate Cores Using Alumina Nanoparticles

The purpose of this research is to investigate the use of alumina nanoparticles (NPs) in low-salinity brine for enhanced oil recovery in carbonate oil reservoirs. A set of analyses including oil/water interfacial tension (IFT), zeta potential, and rock wettability were performed to choose optimized dispersions for spontaneous imbibition tests. The highest oil/water IFT reduction by 0.3% w/v brine occurred at 80 °C/14.5 psi (from 41.3 to 24.3 mN/m at ambient conditions), whereas upon adding 0.05 wt % alumina, IFT declined to 15.6 mN/m at 60 °C/14.5 psi, implying the dependency of NP performance on thermodynamics. The adsorption energy of 0.05 wt % alumina in low-salinity brine at varying pressures/temperatures was calculated to be 6844 k_BT at 60 °C/14.5 psi and 5753 k_BT at 25 °C/600 psi, confirming that temperature is a more influential parameter than pressure. The wettability analysis revealed a considerable reduction in contact angle from 151 to 65 ± 5° using 0.03-0.05 wt % alumina in low-salinity brine, whereas the reduction by low-salinity brine alone was much smaller. Ion chromatography of core effluents showed no natural presence of anhydrite in the rock texture but sulfate adsorbed to the rock surface during Na₂SO₄ flooding, showing the interaction of sulfate-rich brines with rock Ca²⁺, which was also recognized by zeta potential measurements (rock zeta potential shifts from positive toward negative on adding ions, which implies the formation of > CaSO₄^-). Spontaneous imbibition results showed that adding alumina to sulfate-containing low-salinity brine in the tertiary stage can double the oil production in a shorter time as compared to low-salinity brine alone, proving a synergistic effect with alumina NPs.