(28k) Formulation and Evaluation of Nanofluids for Enhanced Oil Recovery in Tight Carbonate Reservoirs: A Laboratory Study

Oil holds significant global importance as a vital energy resource, accounting for more than 30% of the total primary energy consumption globally. Oil production from conventional oil reservoirs is declining amidst a growing global energy demand. Unconventional oil reservoirs, such as tight carbonate rocks, are significant hydrocarbon reservoirs containing approximately 60% of the world's oil reserves. However, their characteristics, including natural fractures, unfavourable wettability, low permeability, and heterogeneity of rock properties, result in typically low oil recovery using primary and secondary recovery mechanisms. This study investigated the combined effects of formation water with 213,000 ppm salinity, cationic surfactants at a critical micelle concentration of 0.25 vol.%, and three distinct nanoparticle types (SiO₂, γ-Al₂O_3, and Al₂SiO₅) on altering carbonate rock wettability and the resultant enhancement in oil recovery. To assess the surface effects and wetting behaviour of the rock when interacting with various injection fluids, fluid-fluid interfacial tension (IFT) and fluid-rock contact angle tests were performed. The oil displacement efficacy of each injection fluid was investigated through dynamic core flooding experiments, conducted at a constant injection rate of 0.5 cc/min at 75°C. The results indicate that the IFT and contact angle for the formation water are 6.27 mN/m and 84.1°, respectively. However, the lowest IFT and most significant alteration of rock wettability towards water-wetness were observed when 0.25 vol.% surfactant was added to 0.075 wt.% of the respective nanosuspension. The recorded IFT and contact angles for Al₂SiO₅, Al₂O₃ and SiO₂ nanosuspensions are 1.23 mN/m, 67.5°; 2.18 mN/m, 59.1°; and 3.01 mN/m, 60.2°, respectively. The dynamic displacement results showed that injecting 2 pore volumes (2PV) of formation water achieved 38.69% oil recovery of original oil in place (OOIP). Surfactant flooding at 0.25 vol.% increased the oil recovery by 13.71% at 2PV compared to the formation water. Oil recovery was highest at a nanoparticle concentration of 0.075 wt.% for each type tested, with Al₂SiO₅ yielding the best results, followed by γ-Al₂O₃, and SiO₂. The combination of 0.075 wt.% nanoparticles with 0.25 vol.% surfactant further improved recovery, ranking the nanoparticles effectiveness as γ-Al₂O₃> SiO₂ > Al₂SiO₅ based on the surfactant's impact. The optimal strategy for maximized oil recovery was flooding with 0.075 wt.% Al₂SiO₅ concentration and 0.25 vol% surfactant concentration, leading to an increase to 63.05% at 1PV and approximately 80.31% after 2PV injection, demonstrating the efficacy of composite nanoparticles combined with surfactants in enhanced oil recovery from tight carbonate reservoirs.

Keywords: Carbonate reservoirs, enhanced oil recovery, surfactants flooding, nanoparticles, waterflooding, wettability alteration, interfacial tension, contact angle.