Implications of geological carbon sequestration on shallow freshwater aquifers geochemistry

Abstract

The dramatic increase in atmospheric concentrations of CO2 over the last few centuries has led to development of various mitigation efforts aimed at preventing CO2 release into the atmosphere. The most promising mitigation technique, in terms of scale and storage potential, is geological carbon capture, utilization and storage (CCUS). However, while acting to solve one environmental problem, CCUS operations are accompanied by other environmental concerns associated with CO2 and brine leakage from injection formations. In this work, the impact of brine leakage on freshwater aquifer quality was examined in terms of water quality standards for drinking water and plant yield reductions due to irrigation with saline waters. These hazards were assessed through a statistical analysis of saline aquifers geochemistry, and applying a simple freshwater-brine mixing model. The impact of CO2 leakage on carbonate aquifers was addressed by conducting a series of pressurized experiments. In these experiments, natural carbonate rocks of different compositions were reacted in water under high partial-pressures of CO2, and the dissolution products analyzed for trace metals. To gain insight into the sources of released metals, the pressurized experiments were coupled with thorough characterization of mineralogy and trace element content in the rocks. The experimental work was supplemented with geochemical modeling, both equilibrium and kinetic (predictive).