**6. Conclusions**

Osmosis-associated imbibition has strong effects on fluid flow in porous mediums in unconventional formations. Those effects are important to be related to production after hydraulic fracturing and during the water-flooding process. Wettability and clay content are the main factors in the imbibition behavior of unconventional formations. Wettability can impact capillary pressure, which is one of the driving forces of imbibition. Clay content has a strong relationship with osmotic pressure. Therefore, understanding those factors can distinguish the dominant mechanism of fluid flow in unconventional reservoirs.

Although imbibition has been extensively studied in formations, it is necessary to further investigate its impact in unconventional formations, especially after hydraulic fracturing treatment. The effect of osmosis on imbibition was neglected before; however, more evidence has shown that osmosis has a significant impact on the fluid flow in clayrich formations, such as shale. Thus, more experimental investigations are necessary to prove its effect, such as high-pressure and high-temperature reservoir conditions with tight pore space. From these further investigations, some insights can be drawn, such as how osmosis-associated imbibition affects the production, and how to manage and control it.

In addition, the numerical modeling for a multi-mechanistic imbibition process has shed some light on the interplay of multiple forces during the imbibition process, especially the changes between capillary pressure and osmotic pressure. The simulation results matched the experimental measurements and field observations, such as the dynamic changes in salt concentration in laboratory and low flow-back recovery in the field. However, further investigations are recommended for simulations under reservoir conditions to match the actual production data with proper upscaling from laboratory-based modeling.

**Author Contributions:** Resources, X.L.; Supervision, Z.Z.; Writing—original draft, review, and editing, Z.Z., X.L. and T.W.T. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by National Natural Science Foundation of China (Grant No. 51974338).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Data sharing not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.
