Progress and prospects of the shallow groundwater responding to CO₂ geological storage

To clarify the potential impacts of large-scale CO₂ injection and the leakage of injected CO₂ along with reservoir brine on shallow groundwater, thereby supporting risk prevention and control for leakage in CO₂ geological storage projects and the protection of shallow groundwater. A comprehensive literature review was conducted to systematically summarize research progress on the impacts of large-scale CO₂ geological storage injection and reservoir fluid leakage migration on shallow groundwater flow fields and water quality. Large-scale CO₂ injection leads to reservoir pressure accumulation and pressure disturbance transmission into shallow aquifers, resulting in groundwater level rise, increased pore pressure, and enhanced evapotranspiration. The leakage of CO₂ or reservoir brine to shallow aquifers can lead to a decrease in pH and ORP, an increase in alkalinity and electrical conductivity, elevated concentrations of major ions, release and migration of toxic trace metals, and alterations in the biodiversity and metabolic diversity of microbial communities. These complex biogeochemical processes are influenced by the intensity of CO₂ and reservoir brine leakage and the hydrogeological conditions of the shallow aquifer. Adsorption and desorption, dissolution and precipitation, and redox reactions are the primary mechanisms governing changes in groundwater quality following CO₂ intrusion. Shallow groundwater serves not only as a risk receptor for potential leakage in CO₂ geological storage projects but also as an information carrier for assessing storage safety and effectiveness. Therefore, greater emphasis should be placed on researching the impacts and monitoring of shallow groundwater in large-scale CO₂ geological storage projects, both to prevent environmental incidents and to provide support for verifying storage effectiveness.