Laboratory Study on the Oil Displacement Process in Low-Permeability Cores with Different Injection Fluids

Although flooding technology has found wide application in low-permeability reservoir development practices, the oil recovery enhancement mechanisms for different injection fluids still lack specific focus based on comprehensive investigations. Therefore, in this paper, supercritical CO₂ (ScCO₂), N₂, and water injection processes in oil-saturated low-permeability tight cores were comparatively studied. To reveal the effect of physicochemical properties of the injection fluid on the oil recovery efficiency, the Berea sandstones with three permeability levels and kerosene were employed in this study to exclude other parameter influences. The flooding processes employing various injection media were investigated based on quantitative comparisons of the oil recovery factor and the displacement pressure difference at two system pressures. The experimental results show recovery efficiencies of 59-91 and 84-92% with the increasing permeability for the ScCO₂ injection process at system pressures of 15 and 25 MPa, respectively, which are much higher than 26-40 and 21-52% in the N₂ case and 43-46 and 45-49% in the water cases. Interfacial tension (IFT) measurement results indicate that miscibility conditions have been achieved for the ScCO₂/oil system, thus leading to much higher oil recovery. On the other hand, the pressure difference results show a similar magnitude of 10 MPa/m for both ScCO₂ and N₂ processes, which is much lower than the 100 MPa/m for the water flooding cases. Comprehensive comparison shows that ScCO₂ shows great advantages in the application of unconventional reservoirs. It is expected that our research work could enrich the investigations of CO₂ flooding and the in-depth understanding of the mechanisms and better guide the utilization of CO₂.