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Characteristics of sorption and distribution of water in nanoporous shale are topics of great interest to evaluate unconventional reservoirs. Also, a study of surface force of water/solid interaction at nanoscale is significant for understanding the storage of initial water and the fate of residual treatment liquid in shale systems. In this work, the thickness and stability of water film were investigated by vapor sorption experiments on clay and shale samples. Meanwhile, an approach based on surface forces (disjoining pressure), which resulted in the instability of adsorbed film transition into condensed bulk liquid, was developed to describe molecule/pore wall interactions. Our experimental results directly demonstrated the occurrence of capillary condensation in hydrophilic clay minerals; however, water would not entirely fill in shale nanopores even under high-moisture conditions. This remarkable finding is mainly due to the inaccessibility of water molecules to micropores of hydrophobic organic matter. In addition, the water distribution characteristics are also significantly influenced by pore scale. Under a moist condition with certain relative humidity (e.g., RH = 0.98), the water distributed in hydrophilic inorganic pores with different sizes was mainly classified as (i) capillary water in small pores (e.g., <6–7 nm) and (ii) water film in large pores (e.g., >6–7 nm). In contrast, the surface repulsion prevents water condensing and likely results in a monolayer water film sorption in hydrophobic organic pores (e.g., θ = 100°). Therefore, in an actual shale system with initial moisture content, the inorganic microporosity totally blocked by water might be incapable of gas transport or storage, while the hydrophobic organic pores mainly provide effective space for gas accumulation.

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Previous attempts to characterize the gas transport through inorganic nanopores were not fully successful. The presence of an adsorption water film within nanopores is generally overlooked. Moreover, the compound influences of moisture content and confinement effect on critical properties of the gas phase have not been considered before. With the intent of overcoming these deficiencies, a fully coupled analytical model has been developed, in which complex bulk-gas transport mechanisms, moisture content, confinement effect, and various cross-section shapes of nanopores are incorporated. Results show that the confinement effect will significantly enhance the apparent gas permeability when the pore radius is smaller than 5 nm, and the real-gas effect can achieve an average increase of 4.38% when the pore radius falls in the range 1−2 nm. The stress dependence will greatly decrease the apparent gas permeability and the corresponding degree for slitlike inorganic nanopores will slightly increase with the increasing aspect ratio.