Effects of Interfacial Molecular Structures on Pressure-Driven Brine Flow in Silica Mesopores

In this work, we conduct molecular dynamics simulations to investigate pressure-driven brine flow in silica mesopores under typical reservoir conditions (323 K and 20 MPa). While surface counterions accumulate strongly in the vicinity of fully deprotonated silica surfaces, water forms multilayer structures due to hydrogen bonding, counterion hydration, and excluded-volume effect. Brine flow behaviors exhibit adsorption, transition, and bulk-like regions in fully deprotonated silica mesopores, while the transition region is negligible in fully protonated ones. In the adsorption region, strong surface hydrogen bonding and a high degree of counterion hydration collectively hinder water mobility. Even without surface hydrogen bonding, persistent ion hydration impedes water flow, leading to the transition region in fully deprotonated silica mesopores and higher viscosity of brine (with 10 wt % NaCl) in the bulk region. This work elucidates the collective effects of surface chemistry and interfacial water structures on brine flow behaviors in silica mesopores from molecular perspectives.