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Geological carbon storage is considered to be an effective measure to mitigate climate crisis. The method in which CO2 is stored depends on its phase state and the depth at which it is injected. In this study, the fault-reservoir system is constructed to elucidate the fault leakage behaviors and CO2 migration in different geological storage environments. Whether CO2 is buoyant or sinking depends on the fluid density difference between CO2 and H2O. When carbon dioxide is injected into deep saline aquifer, CO2 would preferentially migrate upward along the fault plane due to CO2 buoyancy forces, and CO2 plume accumulates beneath the caprock and floats at the top of the reservoir eventually. For CO2 storage in deep ocean reservoir and volcanic basalt, no upward migration of CO2 plume is observed during carbon storage. Fault plane is the preferential pathway for carbon downward transportation during ocean-based CO2 storage, providing a virtually unlimited environment. Compared with deep ocean storage, the much shorter sinking times makes volcanic basalt for carbon storage safer and more effective. It is illustrated that the fluid density difference between CO2 and H2O is the decisive factor in determining CO2 sinking velocity. This investigation of searching CO2 sinking reservoirs provides a promising alterative reference for remove and storage large volumes of the greenhouse gas. [ABSTRACT FROM AUTHOR]

Under the new development philosophy of carbon peaking and carbon neutrality, CO2 and O2 in situ leaching (ISL) has been identified as a promising technique for uranium mining in China, not only because it solves carbon dioxide utilization and sequestration, but it also alleviates the environmental burden. However, significant challenges exist in assessment of CO2 footprint and water‐rock interactions, due to complex geochemical processes. Herein this study conducts a three‐dimensional, multicomponent reactive transport model (RTM) of a field‐scale CO2 and O2 ISL process at a typical sandstone‐hosted uranium deposit in Songliao Basin, China. Numerical simulations are performed to provide new insight into quantitative interpretation of the greenhouse gas (CO2) footprint and environmental impact (SO42–) of the CO2 and O2 ISL, considering the potential chemical reaction network for uranium recovery at the field scale. RTM results demonstrate that the fate of the CO2 could be summarized as injected CO2 dissolution, dissolved CO2 mineralization and storage of CO2 as a gas phase during the CO2 and O2 ISL process. Furthermore, compared to acid ISL, CO2 and O2 ISL has a potentially smaller environmental footprint, with 20% of SO42– concentration in the aquifer. The findings improve our fundamental understanding of carbon utilization in a long‐term CO2 and O2 ISL system and provide important environmental implications when considering complex geochemical processes. [ABSTRACT FROM AUTHOR]