A monitoring strategy to detect CO2 intrusion in deeper freshwater aquifers

The study provides guidance for the design of site-tailored monitoring protocols at CO2 storage sites. Monitoring of geochemical changes induced by CO2 intrusion in freshwater aquifers which are located between storage formations and close-to-surface compartments can enable the early detection of CO2 leakage events and ensure the safety of freshwater resources. The suitability of the hydroelectric conductivity (EC), the total inorganic carbon (TIC) concentration, and the pH of groundwater, which have been proposed as monitoring parameters for shallow aquifers, are investigated by means of reactive scenario modeling at depths between 10 and 450 m. Simulation results suggest that all parameters are well suited and allow distinguishing intrusion of CO2 from intrusion of high-salinity water or a mixture of both. However, EC may not be well-suited for the monitoring of shallow mature clastic aquifers. The study proposes to consider the combination of geophysical and geochemical measurements in site-specific monitoring protocols.

► Monitoring parameters to detect CO2 intrusion in freshwater aquifers are identified.
► Virtual reactive models of mineral–water–CO2 interaction in maximum depth of 450 m.
► Suited parameters are pH, hydroelectric conductivity and total inorganic carbon.
► Bipartite monitoring approach is proposed.
► Approach comprises surface geophysical and in situ chemical measurements.