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+CH4+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+CH4+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+CH4+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. (c) 2022 Elsevier B.V. All rights reserved.