Molecular insights into interfacial behavior of crude oil-brine-quartz systems under brine dilution
Abstract
The influence of brine dilution on interfacial behavior in sandstone reservoirs remains inadequately understood. In this study, molecular dynamics simulations were conducted to elucidate the effects of brine dilution on the wetting behavior of three crude oil systems containing O-, N- and S-bearing heteroatoms. Quartz was adopted as a model sandstone mineral, and the investigation centered on contact angles, fluid density distributions, radial distribution functions, interaction energies, and hydrogen-bonding interactions. The results showed that decreasing brine salinity enhanced quartz hydrophilicity. Contact angles decreased with dilution in O- and N-bearing oils, while the S-bearing system exhibited a non-monotonic trend; however, the overall changes were minor. A water film consistently formed between oil droplets and quartz, thickening with decreasing salinity, which lowered oil-quartz interaction and crude oil density near the surface. Alkanes tended to deplete near the interface, while aromatics preferentially accumulated in this region, although a portion of the aromatics could still migrate into the bulk phase. The relationship between near wall non-hydrocarbon density and contact angle varied by oil type– positive for O- and S-containing oils, negative for N-containing oils. Brine dilution also strengthened water quartz interactions through increased hydrogen bonding, further reducing oil adhesion. Despite these effects, the contact angles in all systems exhibited minimal changes upon brine dilution and remained within the strongly water-wet state. Thus, in reservoirs with inherent water-wet conditions, brine dilution alone is unlikely to significantly enhance oil recovery.
Document Type: Original article
Cited as: Cheng, Z., Xiao, M., Tong, S., Zhang, S., Miao, Y., Xiao, M. Molecular insights into interfacial behavior of crude oil-brine-quartz systems under brine dilution. Capillarity, 2026, 18(1): 14-26. https://doi.org/10.46690/capi.2026.01.02
DOI:
https://doi.org/10.46690/capi.2026.01.02Keywords:
Quartz, wettability, brine dilution, molecular dynamicsReferences
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