Abstract: Shale oil reservoirs in the second member of Funing Formation (Fu-2 Member), Subei Basin are characterized by nanoscale pores and complex pore structures, which impede penetration by conventional fluid systems and result in low imbibition recovery. To address this problem, spontaneous imbibition experiments were conducted using field downhole core samples through systematic core petrophysical tests and crude oil composition analysis, combined with online nuclear magnetic resonance (NMR) scanning technology, and the oil displacement behavior of nanoemulsion in the reservoirs of the Fu-2 Member were clarified. The experimental results show that the nanoemulsion systems effectively promote the imbibition oil recovery process of shale by reducing the oil-water interfacial tension and altering the rock wettability. Compared with conventional base fluid, the nanoemulsion systems CNI-1 and CNN-1 significantly improve the imbibition recovery, increasing by 17.5 and 15.5 percentage points, respectively. In addition, microfractures appear on the shale surface during the hydration process, and the complexity of microfractures increases with the extension of hydration time. The mass of shale cores increases rapidly in the initial immersion stage (0–7 d); then the growth rate slows down significantly (7–21 d) and finally tends to be stable. The research results have been tested in the field of Well Ji 1901 and achieved a significant production enhancement, which provides a theoretical basis and practical guidance for the exploration and development of shale oil in Subei Basin.