In the late stage of unconventional oil and gas fracturing development, the production decreases rapidly, and spontaneous imbibition can effectively improve oil and gas recovery. Spontaneous imbibition mostly relies on external imbibition agents, and there are few studies on the direct use of clean fracturing fluid and the effect of its spontaneous imbibition. This work systematically studies the imbibition performance of clean fracturing fluid and its gel breaking liquid. To find the key factors for the imbibition recovery, the effects of concentration, temperature, and salinity were studied. The results indicate that, with the reduction of concentration and increases of temperature and salinity, the imbibition recovery can be improved. To clarify the imbibition mechanism, the performance, including spontaneous imbibition, interfacial tension, and wettability, of clean fracturing fluid and its gel breaking liquid was evaluated and compared. The results show that the gel breaking liquid contains some surfactant molecules, showing good wettability alteration, emulsification, and interfacial activity. The spontaneous imbibition recovery of the gel breaking liquid is the highest compared with that of fracturing fluid and simulated water. Finally, the T 2 spectrum and 1H NMR image of the core before and after imbibition are obtained, revealing the micro imbibition mechanism of the gel breaking liquid. The gel breaking liquid can enter the small pores through the capillary force, discharge the crude oil into the large pores through the small pores, finally gather and discharge. Therefore, the gel breaking liquid has the characteristics of little damage and low viscosity, making it easy to enter micropores and help to improve oil production through spontaneous imbibition. It can give new ideas and methods for improving production capacity in the later stage of fracturing development.

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