Characterization and optimization of oil–gas interfacial tension during CO2/N2 injection in heavy oil reservoirs: Experimental study and regression model

CO₂/N₂ injection in heavy oil reservoirs has been demonstrated to enhance oil recovery (EOR) and facilitate CO₂ capture, utilization, and storage (CCUS). Interfacial tension (IFT) is a crucial parameter for characterizing oil recovery, but it can be influenced by real-time changes in reservoir pressure and temperature during gas injection. The impact of the CO₂/N₂ ratio on the oil–gas IFT under varying temperature and pressure conditions remains unclear. Therefore, a systematic study was conducted to investigate the effects of multiple parameters on the oil–gas IFT during development processes, and a three-dimensional (3D) database and a regression model of IFT were established using experimental data. The results show that IFT is strongly correlated with density difference, moderately correlated with pressure and CO₂ proportion, weakly correlated with saturates content and resin content, and nonlinearly correlated with temperature, aromatics content, and asphaltene content, respectively. Moreover, it has been observed that an increase in pressure or CO₂ proportion can lead to a reduction in IFT. However, the impact of temperature changes on IFT varies across different pressure ranges. We introduce a new parameter, the equivalent interfacial tension pressure during temperature changes (EITP), to characterize this effect and discuss the reasons for the emergence of EITP, providing new insight into optimizing the CO₂/N₂ injection ratio in the reservoir. This study aims to reveal the advantages of oil–gas interface characteristics under the influence of multiple parameters in promoting low-carbon and efficient development of heavy oil reservoirs, and to explore the significance of CO₂/N₂ for enhancing heavy oil recovery.