Applicable flow regimes and diffusion as well as nano-pore capillary and surface force interactions are topics of great interest for fluid flow in unconventional reservoirs. Liquid flows in shale nano-pores have been wholly less subject to investigation than gas flows. Yet, the study of liquid and multi-component flows at the nano-scale is very important for understanding the interaction of free and bound water with hydrocarbons in shale systems, liquid-driven core analysis methods, and the fate of injected liquids (such as “fracking fluids”) into the reservoir. The Young-Laplace equation for capillary pressure and the Washburn equation for imbibition rate are successfully applied in conventional media and have been applied to shale as well. Pore sizes are on the order of nanometers in shale, a scale that is theorized to mark a threshold for new transport phenomena considerations. This work investigates imbibition with various fluids - ketones, alcohols, aqueous solutions, and alkanes - at the nano-scale and reveals compelling evidence that long range intermolecular, electrostatic, and solvation surface interactions play a significant role in nano-capillary imbibition. Experiments are conducted in a pore size distribution of unconnected, fabricated silica and borosilicate glass nanochannels, which serve as a proxy for water-wet nano-pores in shale. The calculated capillary pressures based on the directly measured experimental results for imbibition lengths differ from the macroscopically predicted results by one order of magnitude. Additionally, in many fluid cases, the trend of the capillary pressure curves derived from the data show a decrease in capillary pressure with a decrease in channel size, or a “dewetting trend.” This trend is contradictory to the prediction of the Young-Laplace formula. Accordingly, as the size of the pores decreases the relative scale of surface interactions increases, possibly leading to a departure from a regime dominated by Laplacian pressure to one strongly influenced by disjoining pressure. A positive correlation is found between the saturation of the imbibing fluid into the bundle of nanochannels and the calculated, unique disjoining pressure of the fluid.
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