Abstract
In the process of CO2 geological sequestration, there is a risk that CO2 will leak into groundwater, resulting in a series of physical and chemical reactions, with influence on chemical compositions of groundwater. In this work, numerical simulation is conducted to study the influence of CO2 migration on the chemical composition of groundwater. The modeling results indicated that when CO2 leaks into groundwater, gaseous CO2 will migrate upward and diffuse laterally under the effect of buoyancy. The acidity of groundwater is enhanced and the pH is significantly reduced, leading to dissolution of calcite, illite, oligoclase, K-feldspar, chlorite and hematite, and precipitation of quartz, kaolinite, smectite-Na, siderite and smectite-Ca. The porosity of the formation increases. The concentrations of K+ and Fe2+ in groundwater gradually increase, the concentrations of Ca2+ and HCO3− basically remain unchanged after increasing to a certain value, the concentrations of Mg2+ and AlO2− first increase and then decrease, and the concentrations of Na+, Cl− and SO42− first decrease slightly and then gradually increase, but the change in concentration is small. Therefore, Fe2+, Mg2+, Ca2+ and pH can be used as important monitoring indicators of whether CO2 leakage into groundwater during geological storage.
Highlights
With the increasing concerns on global warming, CO2 geologic sequestration has been considered to be one of the most effective ways to reduce CO2 emissions and alleviate global warming (Kharaka et al 2011)
Carroll et al (2009) conducted reactive migration modeling on the impact of CO2 intrusion into American plateau aquifers, and showed that CO2 migration in aquifers can be detected by pH and carbonate chemical changes, and pointed out that the most appropriate monitoring location was the bottom of the waterproof roof
Kim et al (2010) evaluated the application of 222Rn in groundwater as a tracer for monitoring CO2 plume migration on shallow groundwater, and the results indicated that 222Rn could be used as a sensitive tracer to directly monitor CO2 leakage
Summary
With the increasing concerns on global warming, CO2 geologic sequestration has been considered to be one of the most effective ways to reduce CO2 emissions and alleviate global warming (Kharaka et al 2011). The study showed that high alkalinity and carbonate minerals mitigate the effects of CO2 intrusion on pH, and no migration of trace elements in the aquifer was observed, but the migration of As, U and Pb was observed in other saline aquifers They suggested that geochemical conditions determine the changes in the water quality of the aquifer and affect the effectiveness of detecting CO2 migration. By analyzing the influence of CO2 migration during geologic sequestration on the chemical components in shallow groundwater, we can screen out monitoring indicators that are more sensitive to changes of CO2 migration, and provide basis for similar CO2 geological storage monitoring programs, and reduce the possible risks in carbon capture and storage (CCS) projects
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