Numerical Simulation of Partitioning and Storage of Impure CO₂ in a Saline Aquifer at the Shenhua CCS Site, China

Carbon capture and storage (CCS) is a key technology to control emissions of CO2 and mitigate climate change. Coinjection of CO2 with major impurity (i.e., N-2 or O-2) into saline aquifers would be an economical strategy. To assess the feasibility of coinjection, the partitioning and storage efficiency of impure CO2 in a deep saline aquifer were numerically investigated using a two-dimensional (2-D) radial anisotropic model, the aquifer condition referred to that of the Shenhua CCS site in the Ordos Basin. The results indicated that a high concentration of impurity moderately accelerated CO2 migration, and the formation dip angle dramatically promoted the migration as well as high temperature. Meanwhile, the partitioning of CO2 with impurities became intensive with the increase of impurity concentration. N-2 could be a suitable tracer to monitor leakage in saline aquifers, since the hysteresis of the breakthrough time between CO2 and N-2 was more evident. Moreover, N-2 lowered the storage efficiency of gaseous CO2, and the lowering was more obvious with the rising formation dip angle and temperature. The impact of N-2 on the storage efficiency of gaseous CO2 was obvious compared to O-2 under the same concentration. The investigation could be crucial for assessing the feasibility of coinjection and the long-term performance of the saline aquifer storage system.