AQUIFER DISPOSAL OF CO2-RICH GASES - REACTION DESIGN FOR ADDED CAPACITY

Aquifer disposal of CO2 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 CO2. The conclusions are general and may be applied to any aquifer. Brines absorb less CO2 due to the salting out effect. The reactions between CO2, 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 CO2 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 CO2 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 CO2 due to this water-rock interaction has been found to be significant compared to that captured by simple solution of CO2 in water. Reaction of aqueous CO2 with calcium and magnesium bearing basic minerals in a siliciclastic aquifer can substantially increase the capacity of the aquifer for CO2 disposal as compared to other aquifer mineralogies.