COMPARISON OF CARBON DIOXIDE SOLUBILITY MODELS UNDER GEOLOGIC SEQUESTRATION CONDITIONS

Carbon dioxide is an important greenhouse gas that has steadily increased in the atmosphere since the industrial revolution. The burning of fossil fuels has largely contributed to this increase, which has impacted global climate change. Organizations worldwide have been researching different methods of mitigating atmospheric carbon dioxide release to the atmosphere in order to stabilize the atmospheric concentration. One of the most promising methods proposed is carbon sequestration in geologic formations, where supercritical carbon dioxide is pumped deep underground and sealed there under impermeable cap rocks. In order to assure that the capacity of the formation is not exceeded, the amount of supercritical carbon dioxide a formation can hold through free-phase and solubility trapping must be predicted accurately. One of the most important variables needed to predict the capacity of the geologic formations to trap carbon dioxide is the concentration of carbon dioxide in the basinal brines. There are many models available that can be used to predict this value. However, the elevated pressures, temperatures and salinities encountered in most geologic formations make this estimate difficult. Here we test three commonly used models by comparing model results to actual experimental data under a range of conditions suitable for geologic sequestration. The models chosen for testing represent a range of computational difficulties. One model is a highly complicated iterative model. The second model is simpler than the first and is correlation based. The third model is an ultra simple model with four adjustable parameters. Results of this study suggest that the iterative model is consistently more accurate, followed by the combination model, and then by the ultra simple model, although all three models seem to fall within an acceptable accuracy range under most conditions appropriate for sequestration in geologic formations.