Molecular Dynamics Study on the Effect of Low-Salinity Water on Crude Oil Desorption from Quartz Surface

To investigate the microscopic regulatory mechanism of salinity on crude oil desorption at the quartz interface in tight sandstone reservoirs, adsorption models of four-component crude oil (acetic acid, toluene, heptane, decane) on quartz and oil-water-rock desorption models under different salinity gradients were constructed. Molecular dynamics simulations were performed, with multi-parameter analysis including relative concentration profiles, interaction energy, and centroid distance. The mechanism of salinity-crude oil component competitive adsorption was systematically elucidated. Results show that the adsorption stability of crude oil components on quartz follows the order: acetic acid > toluene > decane > heptane; Low-salinity water drives efficient crude oil desorption through the synergistic effect of electrical double layer expansion and ion bridging-induced dissociation, while high-salinity water causes delayed and incomplete desorption due to ion barrier and polarity shielding effects; The desorption efficiency ranks as low-salinity water > medium-low salinity water > deionized water > medium-high salinity water > high-salinity water. This study reveals the molecular mechanism of salinity gradient regulating crude oil desorption, providing a theoretical basis for low-salinity waterflooding in tight sandstone reservoirs.