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Wettability of Hybrid Nanofluid-Treated Sandstone/Heavy Oil/Brine Systems: Implications for Enhanced Heavy Oil Recovery Potential

Sun, Xiaofei, Zhang, Yanyu, Chen, Guangpeng, Liu, Tailin, Ren, Dounan, Ma, Jianyun, Sheng, Yukang, Karwani, Sabrina
Energy & fuels 2018 v.32 no.11 pp. 11118-11135
adsorption, aluminum oxide, contact angle, exposure duration, fuels, models, nanofluids, nanoparticles, nonionic surfactants, oils, salinity, sandstone, scanning electron microscopy, silica, titanium dioxide, wettability
In this work, we investigated heavy oil/brine systems on oil-wet sandstone surfaces to quantify the performance of hybrid nanofluids (HNFs) for wettability alteration. In the first step, nanofluid stability analysis was conducted to screen effective single nanoparticles for formulating HNFs and ensure that the properties of the formulated HNFs did not change during the experiments. Then, the ability of HNFs to change the wettability of oil-wet sandstone surfaces to a water-wet state was systematically examined and compared with five types of single nanofluids by contact angle measurements. Then, the effects of HNF composition, hybrid nanoparticle concentration, salinity, and exposure time on the wettability change of sandstones were investigated. Finally, the mechanisms for the wettability shift by HNFs were proposed and verified by scanning electron microscopy visualizations. The results showed that the SiO₂ + Al₂O₃, SiO₂ + TiO₂, and Al₂O₃ + TiO₂ nanofluids could maintain their stability in the harsh reservoir conditions and that they efficiently induced the wettability change of oil-wet sandstone surfaces to a strongly water-wet state under all operational conditions. The SiO₂ + Al₂O₃ nanofluid achieved the highest wettability alteration efficiency (from 156° to 21° at 0.1 wt % HNF). The efficiency was improved by adding a nonionic surfactant and increasing the hybrid nanoparticle concentration, salinity, and exposure time. However, beyond a certain value, the efficiency slightly decreased due to the instability of the HNFs. Two adsorption kinetics models were applied to predict the measured contact angles at different concentrations and exposure times with good agreement. The stronger adsorption of hybrid nanoparticles on sandstone surfaces was considered to be the underlying mechanism for the higher efficiency of HNFs for the wettability shift than that of single nanofluids.