Geochemical Modeling of Changes in Storage Rock Environments at CO2 Injection Sites

Abstract

Geochemical modeling in TOUGHREACT code was used to simulate chemical processes in CO2–rock–brackish water systems in a pilot research environment of CO2 storage in the Brodske area (Czech Republic). Models studied mineralogical changes in rock samples resulting from acidification of the aqueous phase caused by the dissolution of pressurized supercritical CO2. Rock samples of the reservoir horizon and cement from the grouting of an injection borehole were considered, and the water phase represented the mineralized groundwater. The aim of the study was to characterize the influence of CO2 in the geological structure on mineralogical rock changes and to predict gas distribution through the rocks bearing brackish water. The most important chemical processes are dissolution of carbonates and clay minerals during the injection of CO2 into the structure, as the increase in porosity in the structure affects the sequestration capacity of the reservoir rock. In the CO2–cement–brackish water system, the models confirm the rapid dissolution of portlandite and its replacement with calcite. The CSH gel is also dissolved, and silica gel appears. The porosity of the cement decreases. Further studies on such a cement slurry are needed to prevent the possibility of mechanical damage to the integrity of the borehole.