Numerical Study on the Field-scale Aquifer Storage of CO2 Containing N2

Abstract

The possibility of co-injecting these gaseous compounds with CO2 to decrease the operational cost of carbon capture and storage by lowering the requirement of CO2 capture or adding impurities is being considered. Some studies have analyzed the possible geochemistry effects of impurities such as H2S and SO2. However, few studies have focused on the effect of N2 or other non-condensable gas impurities in CO2 stream. Accordingly, this study performed some preliminary numerical simulations on the migration process of CO2/N2 mixture. A modeling tool was established based on the pressure-volume-temperature, viscosity, solubility, and relative permeability characteristics, as well as on the capillary pressure curve, geochemistry model, and COMSOL-Multiphysics software. Then, the migration processes of different N2/CO2 mixtures were evaluated using the modeling tool. The numerical simulation results showed the following: 1) co-injection of CO2 and N2 decreased the storage capacity of CO2 in the aquifer; 2) CO2 plume with N2 moved faster than pure CO2 plume, and CO2 plume with N2 had a higher gas saturation than pure CO2 plume; and 3) a chromatographic partitioning process occurred during the migration process of the gas mixture, suggesting that N2 in the migration front may be an effective monitoring or warning gas for CO2 leakage given the non-toxicity and inertness of N2.