GEOPHYSICAL MONOGRAPH SERIES, VOL. 183, PP. 249-260, 2009
Quantification of CO2 trapping and storage capacity in the subsurface: Uncertainty due to solubility models
The purpose of this chapter is to examine how different solubility algorithms provide different estimates of storage capacity
assessments and lead to different assessments of CO2 trapping mechanisms. Secure storage of carbon in deep saline aquifers requires CO2-brine-rock reactions to convert injected CO2 into dissolved species and solid carbonate minerals. Effective characterization of these reactions on the capacity and security
of storage requires accurate representations of CO2 solubility in brine. Several widely used solubility models and the geochemical reaction simulator Geochemist's Workbench©
(GWB) were compared. These models incorporate various fugacity coefficients, interacting parameters, and corrections for nonideal
behavior of the mixtures (H2O-CO2-salt). The solubility models of Duan and Sun  and Spycher and Pruess  agree well with experimental data both in pure water and in saline solutions. The model of Enick and Klara  also produces results in agreement with experimental data if the fugacity coefficient is calculated based on Duan and Sun . The radius of formation necessary to store 3.3 × 1011 kg of CO2 (equivalent to 30 years of CO2 emissions from a 1000-MW coal-fired power plant) for the 60-m thick Rose Run Sandstone ranges from 6 to 28 km, depending
on the solubility model used. Predictions of silicate mineral dissolution and the precipitation of CO2 trapping carbonate minerals also depend considerably on the choice of solubility model. The choice of solubility model has
tremendous impact on sequestration evaluations, especially: predictions of the volume of a formation required for specific
amounts of CO2, assessments of hydrodynamic, mineral, and solubility trapping mechanisms, and forecasts of density-driven flow patterns.
Complementary to this study, the next chapter in this volume explores how simulations of flow and transport processes are
impacted by choice of solubility model and other equation-of-state components.
Citation: Zerai, B.,