CO2 dynamic mass balance of low permeability reservoir based on “four regions”

In order to limit the increase in global average temperature to 1.5°C, it is necessary to reduce carbon dioxide (CO₂) emissions by 45% by 2030. CO₂ capture, utilization and storage (CCUS) is one of the effective ways to reduce CO₂ emissions. Geological storage of CO₂ provides a solution with the lowest economic cost and the fastest effect for reducing CO₂ emissions. This article proposes a CO₂ storage regional division method based on the characteristics of low-permeability reservoirs in the Yanchang W oilfield in China. The storage space is divided into four regions: gas phase region, two-phase or near-miscible region, diffusion region, and oil phase region. As the displacement progresses, the volume of the gas phase region and the two-phase or near-miscible region gradually increases; the volume of the diffusion region first increases and then decreases. By calculating the storage capacity of each region separately, the total storage capacity is finally calculated. The impact of different pressures and injection rates on dynamic CO₂ storage capacity was evaluated. The results show that pressure and injection rate are positively correlated with total storage capacity. When CO₂ miscible conditions are reached, the increase in total storage capacity will significantly decrease. © 2024 Society of Chemical Industry and John Wiley & Sons, Ltd.