Shale reservoirs contain abundant micro/nanoscale pores, which facilitate capillarity-dominated imbibition as an effective mechanism for enhancing hydrocarbon recovery. During hydraulic fracturing, the penetration of low salinity fracturing fluids can induce clay hydration and swelling, leading to pore structure alterations. However, the effects on imbibition behavior remain insufficiently understood. In this study, high temperature and high pressure imbibition experiments coupled with nuclear magnetic resonance are performed on continental shale. Furthermore, the structural and mineralogical evolution of shale following interaction with deionized water is evaluated by scanning electron microscope. Finally, the pore fracture structure model incorporating clay swelling is constructed and the flow of fracturing fluids is simulated by the lattice Boltzmann method. The results indicate that cores exhibit greater imbibition recovery at higher salinity. The recovery shows a strong positive correlation with pore structure, with denser and less connected pores leading to reduced recovery. Exposed to deionized water, clay is observed to swell and compress both pore space and fracture. After swelling, the flow channels in the two-dimensional model are narrowed or even closed, resulting in fewer effective flow pathways and a reduced swept zone of the oil phase. Meanwhile, the oil phase is prone to snap-off, producing discontinuous droplets that disperse within the pore space. This ultimately leads to a reduction in imbibition recovery after swelling. High salinity effectively suppresses clay mineral swelling and preserves the original pore structure, thereby resulting in higher imbibition recovery. Understanding the imbibition mechanisms under different salinity provides valuable insights for the design of hydraulic fracturing in oilfield applications.

Natural gas hydrates in marine sediments undergo phase transitions under non-equilibrium conditions, making it challenging to accurately measure the permeability characteristics of hydrate-bearing sediments using experimental methods. In this study, pore network modeling is utilized to simulate the hydrate formation process and investigate the single-phase and two-phase permeability of hydrate-bearing sediments, and a comparative analysis was performed on consolidated and unconsolidated sediment samples. The results revealed the evolution of effective permeability as a function of hydrate saturation, and quantitative relationships were observed for the water retention curves and gas-water relative permeability, emphasizing the influence of pore structure and hydrate distribution on flow behavior. On the basis of the simulation results, predictive methods for irreducible water saturation, maximum water saturation, and key parameters in the van Genuchten and Brooks-Corey models for hydrate-bearing sediments are proposed. The findings provide deeper insights into gas-water flow dynamics in hydrate-bearing sediments and offer valuable guidance for hydrate resource exploitation, the assessment of environmental risks associated with hydrate dissociation, and the evaluation of carbon sequestration potential.