In the geological carbon dioxide (CO2) sequestration in abandoned oil reservoirs

there usually exists a fluid system including CO2

oil and brine

where the interplay between them is very important for the successful CO2 storage. In this paper

molecular dynamics simulations were carried out to investigate the interfacial characteristics of the CO2

n-hexane and NaCl solution system with different CO2 fractions at the miscible state. CO2 and n-hexane formed a miscible phase

and a clear interface was observed to separate the CO2 and n-hexane mixture with brine. Both the interfacial width and roughness increased with increasing CO2 composition

indicating the stronger interfacial interactions when water molecules contacted with CO2

leading to the reduction of interfacial tension. The surface adsorption of CO2 reached the maximum when CO2 molar fraction equaled to 65%

as well as the deficiency of n-hexane. This implied the surfactant feature of CO2 and the hydrophobicity of n-hexane towards the interface investigated. A special micro structure was observed at the interface

where CO2

water and n-hexane molecules had own preferred arrangement tendency. The special interfacial characteristics found could explain the experimental IFT phenomena and the microstructure variation in the CO2 injecting process

and could provide some theoretical guidance for CO2 sequestration.