Geochemical Modeling of CO₂ Sequestration in Deep, Saline, Dolomitic-Limestone Aquifers: Critical Evaluation of Thermodynamic Sub-Models

Authors

Mark W. Thomas, University of South Florida
Mark T. Stewart, University of South FloridaFollow
Maya Trotz, University of South FloridaFollow
Jeffrey A. Cunningham, University of South Florida

Document Type

Article

Publication Date

5-4-2012

Keywords

carbon dioxide, carbon capture, sequestration, storage, CCS, TOUGHREACT

Digital Object Identifier (DOI)

https://doi.org/10.1016/j.chemgeo.2012.02.019

Abstract

Geochemical modeling is a common tool to estimate the potential for storing supercritical CO₂ in deep saline aquifers, and to predict the effects thereof. Geochemical models necessarily rely on thermodynamic relationships or “sub-models” to estimate quantities such as chemical solubility, activity, and fugacity. In this paper, we compare three proposed models for the fugacity of supercritical CO₂, four proposed models for the activity coefficient of dissolved (aqueous) CO₂, and four proposed models for the solubility of CO₂ in aquifer brine. We examine the conditions under which estimates from these different proposed thermodynamic sub-models agree or disagree. Also, we develop a geochemical model that predicts the effects of injecting CO₂ into a deep, saline, dolomitic-limestone aquifer; specifically, we predict the change in brine pH, the mineral precipitation/dissolution, and the potential solubility trapping of injected CO₂ in response to the CO₂ injection. We test nine different versions of the model, utilizing different combinations of the thermodynamic sub-models listed above. This allows us to quantify how key geochemical predictions depend upon the selection of thermodynamic sub-models. We find that different combinations of thermodynamic sub-models yield similar estimates for equilibrium pH and for quantities of mineral precipitation/dissolution, but that agreement is worse when predicting the equilibrium CO₂ concentration in brine and/or the solubility trapping of CO₂. These results indicate that the predicted equilibrium pH and mineral precipitation/dissolution are not very sensitive to the underlying thermodynamic sub-models, whereas estimates for the CO₂ concentration in brine and potential solubility trapping are. Overall, the geochemical predictions are least sensitive to the choice of CO₂ activity coefficient sub-model, are moderately sensitive to the choice of CO₂ solubility sub-model, and are most sensitive to the choice of CO₂ fugacity coefficient sub-model.

Was this content written or created while at USF?

Yes

Citation / Publisher Attribution

Chemical Geology, v. 306-307, p. 29-39

Scholar Commons Citation

Thomas, Mark W.; Stewart, Mark T.; Trotz, Maya; and Cunningham, Jeffrey A., "Geochemical Modeling of CO₂ Sequestration in Deep, Saline, Dolomitic-Limestone Aquifers: Critical Evaluation of Thermodynamic Sub-Models" (2012). Civil and Environmental Engineering Faculty Publications. 20.
https://digitalcommons.usf.edu/egx_facpub/20