GROUNDWATER QUALITY CHANGES IN RESPONSE TO CO2 LEAKAGE FROM DEEP GEOLOGICAL STORAGE

CO₂ sequestration into deep reservoirs needs to ensure the safety of overlying groundwater resources. Questions exist whether groundwater could become contaminated by leakage and upward migration of CO_2. The formation of carbonic acid in response to elevated levels of dissolved CO₂ and the resulting decrease in groundwater pH could cause toxic metals to be mobilized through several pathways that include ion exchange, desorption from surface sites, and mineral dissolution. Additional effects could be caused by the transport of co-injected H₂S and/or organic compounds mobilized by supercritical CO₂ at depth. This paper touches on these various questions and discusses results from reactive transport simulations conducted for both hypothetical scenarios as well as for a CO₂ controlled-release field experiment. Model predictions and experimental results suggest that CO₂ dissolution into shallow groundwater can trigger the dissolution of minerals and sorption/exchange reactions, possibly mobilizing trace elements. The leakage of co-injected H₂S into groundwater could exacerbate such potential impacts. Preliminary simulations also suggest that any volatile organic species present in CO₂ storage formations could be readily dissolved by supercritical CO₂ and mobilized to be transported into shallower groundwater.