A study of the effect of impurities on CO2 storage capacity in geological formations

Abstract

Carbon capture and storage (CCS) is a promising technology for reducing atmospheric CO2 emissions from industrial CO2 emitters. The high cost of carbon capture is one of the major barriers to the implementation of CCS. CO2 captured from industrial emitters contains various impurities such as N2, O2, Ar and SOx, and storing the impure CO2 underground would eliminate the need for purification and substantially reduce the cost. However, the impurities may negatively impact CO2 storage. In this work, we studied the impact of impurities on the storage capacity of CO2 in geological formations through density changes. Density measurements for CO2 mixtures with N2, O2, Ar and SO2 were carried out in CO2 storage pressure and temperature ranges. The observed density behaviors and the impact on the storage capacity of CO2 are analyzed. The experimental and analytic results suggest that N2, O2 and Ar would bring about a minimum of the storage capacity at a certain pressure, where about 15mol% N2, O2 and Ar could reduce the storage capacity for CO2 by over 65%. The reduction of the storage capacity decreases with increasing temperature. The results also suggest that Ar could represent the three air-derived impurities combined in density and storage capacity evaluations for CO2 mixtures. Moreover, the results suggest that SO2 could bring about a maximum of the storage capacity, where more CO2 could be stored in given space compared to pure CO2 case. Based on the analysis, a generalization is proposed to predict whether a minimum or a maximum for the CO2 storage capacity would occur with different impurities.