A Review on Hybrid EOR Techniques: The Role of Nanofluids in Low Salinity Water Flooding

Abstract

As global energy demands persist, crude oil remains a dominant energy source despite the maturity of many reservoirs. Enhanced Oil Recovery (EOR) techniques such as chemical, thermal, microbial, low salinity water flooding (LSWF), and nanotechnology offer promising solutions to extract remaining oil economically. LSWF, particularly effective for less viscous crude oils, alters rock wettability and reduces interfacial tension (IFT), especially when sodium chloride concentrations are below 10,000 ppm. The effectiveness of LSWF is influenced by ionic strength, with divalent ions like Ca²⁺ and Mg²⁺ playing distinct roles in secondary and tertiary recovery stages. Combining surfactants with LSW can further reduce IFT and enhance wettability, although challenges such as surfactant loss and degradation at reservoir conditions persist. Recent advancements explore integrating nanoparticles (NPs) with LSW to improve EOR efficiency. Nanoparticles like SiO₂, TiO₂, and Al₂O₃ enhance fluid stability, wettability, and IFT reduction. The high surface-area-to-volume ratio of NPs promotes favourable nanoscale interactions essential for oil mobilization. However, NP stability, influenced by size, surface charge, ionic strength, and hydrophobicity, must be evaluated using tools like zeta potential analysis and DLVO theory. Studies indicate that while SiO₂ NPs offer high stability, their adsorption during transport can limit recovery efficiency. Moreover, the synergy between surfactants and NPs in nanofluids under varying salinity levels demonstrates enhanced oil recovery through improved dispersion and wettability alteration. This study investigates the combined effect of LSW and nanoparticle-assisted EOR, emphasizing NP stability, transport mechanisms, and physicochemical interactions to maximize recovery efficiency under harsh reservoir conditions.