The miscible behaviors of C3H8/C8H18(C7H17N) system in nanoslits: Effects of pore size and rock surface wettability

• The miscible behaviors of C 3 H 8 and C 8 H 18 /C 7 H 17 N in nanoslits are studied by MD simulations. • Increasing pore size could promote the miscible process of C 3 H 8 and C 8 H 18 . • The rock surface wettability has a different effect on the miscibility of C 3 H 8 and C 8 H 18 /C 7 H 17 N. Understanding the confinement effects and the miscibility mechanism of gas and crude oil in nanoslits is of significance for enhancing oil recovery in deep reservoirs. In this study, the effects of pore size and rock surface wettability on the miscible behaviors of hydrocarbon gas and crude oil at 413 K and 60 MPa are investigated. The simulation results indicate that increasing pore size could promote the miscibility of C 3 H 8 and C 8 H 18 , owing to the decreased interactions between C 8 H 18 molecules and the SiO 2 -H surface. In addition, compared with the water-wet SiO 2 -OH surface, it could be clearly discovered that the oil-wet SiO 2 -CH 3 surface shows a stronger confinement effect on the miscible process of apolar crude oil and C 3 H 8 due to stronger interaction between SiO 2 -CH 3 surface and crude oil. In contrast, the interaction between polar crude oil and SiO 2 -OH surface becomes stronger due to the formation of hydrogen bonds, thus reducing the solubility of polar crude oil in C 3 H 8 phase. This study reveals that hydrocarbon gas flooding is suitable for reservoirs with low content of polar crude oil, which could provide valuable guidance for efficient development of deep and ultra-deep reservoirs.