Are Vertical Joints and Fractures Self-Sealing During Bouancy-Driven CO2 Migration in Continental Flood Basalts?

ARE VERTICAL JOINTS AND FRACTURES SELF-SEALING DURING BUOYANCY-DRIVEN CO2 MIGRATION IN CONTINENTAL FLOOD BASALTS?
M. Phukan1, H. P. Vu1, R. Haese1


The permanent disposal of carbon dioxide in the subsurface has been considered a viable mitigation option to reduce global warming. Sedimentary basins have been studied over years as a conventional storage reservoir for CO2 due to presence of caprock, but the mineralisation of CO2 might take thousands of years to occur. Continental flood basalts are considered unconventional CO2 storage reservoirs where interbedded massive basalt zones serve as barriers for upward CO2 migration. However, vertical joints and sub vertical fractures in those massive basalt zones may serve as conduits for buoyancy-driven CO2 migration and thereby pose a risk to CO2 containment. Basalts have high concentrations in Ca-, Mg- and Fe-bearing silica minerals and basaltic glass, which are known to dissolve in low pH, CO2-enriched water. The dissolution of basalt phases consumes protons and leads to an enrichment in dissolved silica and di-valent cations to the point when secondary minerals precipitate. Mineral precipitation in joints and fractures may be sufficient to reduce or fully block fluid flow. This research project will investigate the conditions and capacity of self-sealing of these joints.


Batch reactor and core flood experiments are used to determine the rate of dissolution and precipitation reactions and the required fluid residence time for self-sealing. The kinetics of mineral dissolution is studied in batch reactor experiments, using basalt wafers as the reactive sample immersed in CO2-saturated fluid. Results from fluid analysis shows a rapid increase in cation (e.g., Ca and Mg) concentrations, followed by a significant reduction in those cations suggesting precipitation of secondary minerals. Further, geochemical modelling suggests the formation of clay minerals and zeolites, which could be potential sealants under the conditions of the experiments.


Future experimental work involves core flood experiments to better understand the reactive-transport of CO2-saturated fluid and associated dissolution and precipitation reactions in basalt cores with artificial fractures.