Numerical Simulation Investigation On CO₂/Brine Multiphase Migration In Heterogeneous Porous Media

C02 storage in saline aquifers is considered as the most promising method for CO2 geological sequestration and attracts wide attention of governments and research institutes owing to its widely distributed storage site and huge storage capacity. Understanding the CO2 multiphase mitigation process in porous media is a significant basis to forecast the long-term fate of the stored CO2 and assess the storage capacity of CO2 storage sites. As reservoir rocks are typically features with great heterogeneity, they can influence the multiphase mitigation process of CO2/brine and control the storage behavior. Therefore, the analysis for the effect of heterogeneity of rocks on CO2/brine multiphase mitigation characteristics presents a significant theoretical research value.Wettability and its heterogeneity are key factors that influence multiphase mitigation processes. The simulation on the effect of wettability heterogeneity on CO2/brine multiphase mitigation is carried out by the Lattice Boltzmann method in the paper. The result suggests that the mitigation of CO2 shows apparent selectivity and go through CO2-wet regions preferentially, leading to the formation of fingerings which reduces the displacement stability of CO2 on pore-water and causing that a part of pore-water cannot be driven away and the residual water saturation increases.Cements influence the process of CO2/brine multiphase flow mainly by changing the pore connectivity, narrowing flow channels and causing isolated pores. In this paper, we analyze the influence of pore structure heterogeneity caused by cements on the CO2/brine multiphase flow by the Phase Field method. The results suggest that 1) the influence of isolated pore on multiphase mitigation of CO2/brine is more significant than that of changing connectivity and narrowing flow channel under the condition of the same amount of cements; 2) CO2 flow is not simply restricted by cements, while it will also be promoted in a cement-caused high permeability structure.Pore structure heterogeneity is a key factor that controls the multiphase mitigation process of the CO2 local storage. This paper conducts the analysis of influencing factors on the CO2 local accumulation at the pore scale and reveals the interaction mechanism and the dominant factors of CO2 local sequestration mechanism. The result suggests that 1) the narrow pore throat is the main cause of CO2 local accumulation.; 2) maintaining the throat diameter unchange, the increase of flow channels will reinforce the permeability which can counteract the effect of capillary force on CO2 local accumulation and make the capillary trapping mechanism useless; 3) the effect of connectivity on CO2 local accumulation mainly presents on the region before heterogeneous layer, which can reduce the effective displacement area of CO2 and decrease the CO2 saturation.