Development and evaluation of sustainable ionic liquid-based surfactant formulations for EOR in high-temperature, high-salinity, low-permeability carbonate reservoirs

Designing robust surfactant-based EOR formulations for carbonate reservoirs under high temperature, high salinity, and low permeability (< 10 md) conditions is particularly complex. This study focuses on formulating and evaluating an ionic liquid (IL)-based surfactant system tailored for such environments. A systematic screening workflow was employed to identify the optimal composition. This workflow included stability analysis, emulsification behavior, contact angle measurements, phase behavior evaluation, adsorption critical study, and coreflooding experiments. A newly synthesized imidazolium-based ionic liquid (MDIMO) was blended with amphoteric surfactants and IOS to leverage the tunable and stability characteristics of ILs. The optimized formulation achieved IFT of 0.003 mN/m and contact angles of 50°, while maintaining stability at salinity levels up to 230,000 mg/L and ultrahigh hardness (> 10,000 mg/L). Injection of this IL-based formulation into a low-permeability carbonate core yielded a 19% incremental oil recovery beyond seawater flooding. Moreover, incorporating sodium polyacrylate significantly reduced the adsorption density of MDIMO to less than 1 mg/g on the carbonate rock. Compared to a conventional surfactant blend, the IL-based formulation demonstrated markedly superior performance in IFT reduction, emulsification, and oil recovery. The combined Amott–USBM, contact angle, FTIR analyses, and ζ-potential validated the wettability state and alteration mechanisms. These findings highlight the structure-performance technique and its collaboration with blending approach to develop a formulation for EOR in low permeable carbonate reservoir. This study benchmarks the performance of a bulky synthesized ionic liquid against traditional surfactants for the development of more sustainable and efficient EOR strategies under harsh conditions.