Feasibility Study on Imbibition of Temperature-Resistant Nanoemulsion for Enhancing Shale Oil Recovery

Shale oil has emerged as a vital component of the global energy portfolio, and enhancing its recovery efficiency is indispensable for energy security and sustainable development. In this study, bicontinuous microemulsions were prepared and diluted to form nanoemulsions, with the purpose of investigating their potential for enhancing shale oil recovery. Their performance was systematically evaluated through a series of characterizations, including salinity scanning, particle size distribution analysis, microscopic morphology observation, interfacial tension (IFT) measurement and crude oil emulsification and dispersion tests, as well as spontaneous imbibition (SI) or forced imbibition (FI) experiments on shale core samples. Results showed the nanoemulsions had good salt resistance, with particle size and morphologies being highly compatible with the nanoscale pore structure of shale reservoirs. Notably, the IFT of the nanoemulsion system could be significantly reduced to 10–2 mN/m. They also effectively altered the wettability of rock surfaces from predominantly oil-wet to water-wet. A key finding was that these nanoemulsions maintained transparency and stability without aggregation or phase separation even at 140 °C, thus demonstrating excellent thermal resistance. Specifically, a 0.3 wt % nanoemulsion achieved 34.05% SI recovery, which is 25.22% higher than that of brine, 17.19% higher than that of surfactant systems, and 15.53% higher than that of SDS. Under identical temperature and concentration conditions, injecting 0.5 pore volumes (PV) of the nanoemulsion followed by a 20 h soaking period yielded a recovery efficiency of 32.36%. Furthermore, after two injection cycles, the imbibition recovery efficiency increased to 38.68%, which is 8.36% higher than that of surfactant system, and 7.12% higher than that of SDS. These findings highlight the nanoemulsion’s superior capability in reducing interfacial tension and its significant potential for enhancing shale oil recovery. The developed thermostable nanoemulsion provides a promising technical basis for the efficient exploitation of shale oil reservoirs.