Trace Metal Mobilization in an Experimental Carbon Sequestration Scenario

Mobilizing trace metals with injection of supercritical CO2 into deep saline aquifers is a concern for geologic carbon sequestration. Hydrothermal experiments investigate the release of harmful metals from two zones of a sequestration injection reservoir: at the caprock-reservoir boundary and deeper within the reservoir, away from the caprock. In both systems, Cd, Cr, Cu, Pb, and Zn behave in a similar manner, increasing in concentration with injection, but subsequently decreasing in concentration over time. SEM images and geochemical models indicate initial dissolution of minerals and precipitation of Ca-Mg-Fe carbonates, metal sulfides (i.e. Fe, As, Ag, and Co sulfides), and anhydrite in both systems. The results suggest that Ba, Cu, and Zn will not be contaminants of concern, but Pb, Fe, and As may require careful attention.