Aquifer disposal of CO 2-rich gases: Reaction design for added capacity

Abstract

Aquifer disposal of CO 2 is being investigated in a region between the Genesee and Sundance coal-fired power stations, west of Edmonton, Alberta, Canada. This study considers the changes to the mineralogy and water chemistry of both brackish and briney waters in carbonate and siliciclastic aquifers in this area as a result of the injection of CO 2. The conclusions are general and may be applied to any aquifer. Brines absorb less CO 2 due to the salting out effect. The reactions between CO 2, water and aquifer solids in the carbonate aquifers can largely be described in two steps: dissolution of calcite and adsorption of dissolved calcium on clays. The dissolving CO 2 is neutralized to form bicarbonate ion due to the buffering action of the carbonate dissolution while the effect of ion exchange is to minimize the amount of dissolved calcium. In siliciclastic aquifers, the dissolving CO 2 is neutralized by reactions between basic aluminosilicate minerals (i.e. feldspars) and the resulting, more acid reaction products (i.e. kaolinite). Large amounts of carbonate minerals can precipitate during these reactions. The additional capture capacity of CO 2 due to this water-rock interaction has been found to be significant compared to that captured by simple solution of CO 2 in water. Reaction of aqueous CO 2 with calcium and magnesium bearing basic minerals in a siliciclastic aquifer can substantially increase the capacity of the aquifer for CO 2 disposal as compared to other aquifer mineralogies.