The development of low- and ultra-low-permeability reservoirs presents significant challenges, as conventional chemical flooding agents often fail to concurrently achieve effective wettability alteration and ultra-low oil-water interfacial tension (IFT). Furthermore, static imbibition tests cannot adequately simulate the actual dynamic reservoir development process. In this study, a novel imbibition agent, SL-1, was formulated by compounding nano-SiO? with an anionic-nonionic surfactant. Experiments were conducted using artificial ultra-low-permeability cores (1～5 mD). Fundamental properties were evaluated via contact angle goniometry, spinning-drop IFT measurements, and static imbibition tests. Nuclear magnetic resonance (NMR) T? spectroscopy was employed to quantitatively characterize dynamic imbibition behaviors. The effects of injection rate, matrix permeability, shut-in duration, and fracture geometry (length and density) on imbibition efficiency were systematically analyzed, followed by two field pilot tests. Results demonstrate that 0.3 wt% SL-1 reduces the IFT to the 10?³～10?? mN/m range and alters the wettability of oil-wet quartz surfaces from a contact angle of 107° to 34°, achieving a static imbibition recovery factor of 31%. Dynamic imbibition is governed by multiple factors, with their influence weights ranked as follows: shut-in duration > permeability > fracture length > fracture density > injection rate, identifying shut-in duration and permeability as the dominant controlling factors. Fracture development expands the fluid-rock contact area, enhancing the imbibition recovery factor of cores with through-going fractures by 51.6% compared to intact cores. Field trials validated the efficacy: in Well S1, the daily oil production increased from 0.8 t to a peak of 6.4 t, with a cumulative incremental oil production of nearly 1000 t; in Well S2, production rose from 0.2 t/d to a peak of 2.2 t/d, representing an eightfold increase over pre-treatment levels. The study confirms that the SL-1 nano-imbibition system effectively optimizes reservoir wettability and reduces interfacial tension, significantly improving the imbibition recovery in low-permeability reservoirs and demonstrating considerable potential for field application.