The critical role of mineral heterogeneity in low-salinity water flooding in tight sandstones: Insights from molecular dynamics simulations

The microscopic mechanisms by which mineral composition governs the efficiency of low-salinity water flooding in tight sandstone reservoirs remain inadequately understood. In this study, molecular dynamics simulations were conducted to construct crude oil (acetic acid, toluene, n-heptane, and n-decane)-mineral (quartz, K-feldspar, and kaolinite) adsorption models, along with oil–water–rock desorption models under varying salinity conditions. By analyzing parameters such as relative concentration profiles, binding energies, centroid displacements, and hydrogen bonds, the competitive adsorption mechanisms between dissolved ions and crude oil components were systematically elucidated. The results indicate that polar components (acetic acid and toluene) exhibit stronger adsorption stability on mineral surfaces than non-polar components (n-decane and n-heptane). Due to chain folding optimizing interfacial contact, n-decane shows slightly higher stability than n-heptane. On quartz surfaces, low salinity promotes efficient crude oil desorption through double-layer expansion and disruption of ionic bridges. For K-feldspar, low salinity facilitates desorption via interlayer K+ exchange. For kaolinite, however, electrostatic-dispersive synergistic adsorption restrains desorption under low-salinity conditions, leading to residual acetic acid retention. The adsorption–desorption responses to salinity are controlled by mineral-specific surface heterogeneity, manifested by polar Si–OH groups on quartz, Al–OH2+ sites on kaolinite, and interstratified K+ in K-feldspar, which lead to hydrogen bond breaking, electrostatic-dispersive synergy, and controlled K+ release, respectively. This study clarifies the coupling between mineral type, salinity, and desorption behavior, providing molecular-level theoretical underpinnings for the application of low-salinity water flooding in tight sandstone reservoirs.