Thickness and stability of water film confined inside nanoslits and nanocapillaries of shale and clay

Meanwhile, the phase behavior of adsorbed water film within nanoporous montmorillonite and shale were investigated by water vapor (H2O) adsorption isotherms. Specially, the water distribution characteristics inside single nanopore rather than the whole porous media were also investigated based on the difference of pore size distribution (PSD) between dry and moist samples, and these PSD information was obtained by low temperature (77 K) nitrogen (N2) sorption analysis. Our experimental results directly demonstrated the evidence of water condensation in hydrophilic clay samples, e.g., pores < 6-7 nm would be totally blocked by capillary water. However, a “partial condensation” phenomenon was found in shale samples, e.g., the shale nanopores could not been entirely filled by water even under a high-moisture condition (RH = 0.98), which was mainly caused by hydrophobic repulsion of organic minerals. This surface repulsion could prevent water from condensing and likely result in a monolayer water film adsorbed inside these hydrophobic organic nanopores, e.g. graphite. Therefore, in an actual shale system with initial moisture, the storage of water inside organic pores can be neglected while these inorganic micropores blocked by condensate may be unavailable for gas storage or transport.