Interfacial behaviors of the H₂O+CO₂+CH₄+C₁₀H₂₂ system in three phase equilibrium: A combined molecular dynamics simulation and density gradient theory investigation

The interfacial behaviors in H₂O+gas+oil 3-phase systems are critical for CO₂ near-miscible/immiscible flooding and sequestration processes but require further investigation. In this article, molecular dynamics (MD) simulation and density gradient theory (DGT) with PC-SAFT equation of state were simultaneously conducted to study the interfacial behaviors in the H₂O+CO₂+C₁₀H₂₂ 3-phase system and the effect of impurity gas CH₄ on the interfacial properties at different temperatures (323–423 K) and pressures (up to around 16 MPa). We found reasonable agreement between the estimations from MD and DGT. When the H₂O+CO₂+C₁₀H₂₂ 3-phase system is in contact with CH₄, the interfacial tensions (IFTs) of all three interfaces increase. The increment of IFT is pronounced at low temperatures and high pressures. Remarkably, CH₄ molecules accumulate in all three interfaces. However, the positive surface excesses of CH₄ are smaller than those of CO₂, which may explain the increment of IFT. Moreover, the spreading coefficients S in the H₂O+CO₂+C₁₀H₂₂ 3-phase system are negative indicating the existence of 3-phase contact. The behaviors of S in the H₂O+CO₂+CH₄+C₁₀H₂₂ 3-phase system are similar to those in the system without CH₄. Nevertheless, the effect of temperature on S is little due to the changes of IFT caused by CH₄. These insights could help to enhance the understanding of the effects of impurities on CO₂ enhanced oil recovery methods under geological conditions.