3. Distribution of Water and Hydrocarbon in P-H and H-H Nanopores

Fig. 4 shows the equilibrium configurations and number density profiles (along z-direction) for water and hydrocarbon in 5 nm H-H (Fig.4a-b) and P-H (Fig. 4c-d) nanopores. We do not show the illite structure for clarity.
Fig. 4a shows a water film adjacent to the clay surfaces in the H-H pore system. Water preferentially adsorbs because of the strong electrostatic interaction between water and the surfaces82 and the formation of a hydrogen bond between water and the surface hydroxyl and oxygen groups83. This observation is analogous to water adsorption in silica-based pore structures76,84. Increasing the water concentration to 58.82% as shown in Fig.4b leads to an increase in the adsorbed film thickness. The number density of water (shown in the blue line) and hydrocarbon (black solid line) are relatively constant across the pore.