Threats to the Quality of Water Resources by Geological CO2 Storage: Hydrogeochemical and Other Methods of Investigation: A Review

Abstract

AbstractIn the last decades, geological storage of CO2 is under discussion, in order to reduce emissions of greenhouse gases to the atmosphere, as a contribution to the mitigation of climate change. Deep saline aquifers in sedimentary basins are being considered as the most prominent locations for CO2 storage and sequestration. This chapter provides an overview of recent research regarding CO2 storage with focus on hydrogeochemical methods of investigation, gas–water–rock interactions and monitoring methods as well as potential risks to freshwater resources. The main trapping mechanisms for CO2 in deep geological formations are: (1) hydrodynamic trapping as a supercritical fluid below the caprock, (2) residual trapping within the pores of reservoir rocks, (3) solution trapping as aqueous species dissolved in formation water, and (4) mineral trapping by precipitation of carbonate minerals. However, risks for freshwater resources can arise due to low pH values. As a consequence, the dissolution of minerals is causing high concentrations in trace elements that are potentially dangerous for human health. Another aspect is ascendant saline water which could intrude into shallower fresh water aquifers due to the displacement caused by injection pressure. Hydrogeochemical monitoring methods are recommended to detect possible CO2 leakage.KeywordsCCSCO2-sequestrationGas–water–rock interactionGeological carbon dioxide storageGroundwater monitoringHydrogeochemical modelingHydrogeochemistrySaltwater intrusion