Mineral Precipitation from CO2-Saturated Water in Basalts and its Potential for Self-Sealing of Fractures and Joints

Abstract

Continental flood basalts are considered as potential CO2 storage reservoirs; however, many knowledge gaps have not been addressed. This study determines whether mineral precipitation will seal joints and fractures during the vertical migration of CO2-enriched water and thereby contribute to CO2 containment. The interaction of CO2-saturated water with basalt wafers was studied in a batch reactor at a pressure of 80 bars and 60°C for a period of 44 days. Si-Al-rich minerals such as smectites and zeolites were observed in suspension at the end of the incubation. In addition, mineral precipitation on at the surface of the basalt wafers was identified as magnesite, kaolinite and Mg- and Fe-oxides. Na-rich Si-Al minerals were identified as Na-nontronite, which belongs to the smectite group. All cation concentrations declined between incubation day 6 and 44. Mineral saturation indices have been computed for the experimental solution as a function of time to observe supersaturated and undersaturated mineral phases. Smectites, zeolites, Fe-oxides, and kaolinite are observed to be supersaturated in the experimental fluid till the end of the reaction time period of 44 days which matches closely with the experimental secondary mineral phases. These secondary minerals could be potential sealants and mitigate CO2 leakage issue.