Numerical Simulation of Two-Phase Flow of CO2 -Oil in Pore-Scale at Near-Miscible Condition Using Computational Fluid Dynamic Technique

Carbon dioxide (CO2) gas flooding has long been regarded as a popular method of improving oil recovery as it can reduce the carbon footprint in the atmosphere through carbon storage and CO2 sequestration. Miscible flooding is considered the most efficient way to reach the maximum oil recovery factor. However, not only do not all oil reservoirs experience pressures above miscibility but also due to difficulty in retaining reservoir pressure in the desired region, numerous miscible flooding operations experience pressure decline below minimum miscibility pressure (MMP). In these circumstances, a near-miscible process seems to be attainable and practical compared with a miscible injection. In the current study, we exclusively focus on pore-scale near-miscible CO2-oil displacement. In this regard, the effective near-miscible region is determined based on the available criteria in the literature. Then at the lower-pressure limit of the defined near-miscible region, Phase-Field coupled with the Navier-Stokes equation as the numerical approach is implemented to investigate the CO2-Oil displacement by capturing the diffusive interface properties and hydrodynamic properties of fluids. Quantitative analysis of results, to better realize the pore-scale mechanism of oil recovery demonstrated that if the pressure conditions are maintained throughout the modeling in the effective near-miscible pressure region, almost significant amounts of by-passed oil in the pores from small to large to be recovered and the oil recovery increased from 50% to more than 90% approaching the results of miscible gas injection. This outcome can accentuate the significance of near-miscible CO2-EOR in operation applications.