Abstract

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 C3H8 and C8H18, owing to the decreased interactions between C8H18 molecules and the SiO2-H surface. In addition, compared with the water-wet SiO2-OH surface, it could be clearly discovered that the oil-wet SiO2-CH3 surface shows a stronger confinement effect on the miscible process of apolar crude oil and C3H8 due to stronger interaction between SiO2-CH3 surface and crude oil. In contrast, the interaction between polar crude oil and SiO2-OH surface becomes stronger due to the formation of hydrogen bonds, thus reducing the solubility of polar crude oil in C3H8 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.