Influence of CO2 Leakage On Aquifer Drinking Water Quality From Carbon Sequestration

Of the many proposed methods of mitigating anthropogenic carbon emissions to Earth’s atmosphere, geologic carbon sequestration is the closest to widespread implementation.  Geologic carbon sequestration is designed to mimic the natural long-term storage of CO₂ in deep geologic formations by injection of CO₂ into deep saline aquifers, depleted oil and gas fields or un-minable coal seams.  After injection, buoyancy of the CO₂ will cause vertical migration until the plume reaches a low permeability layer, or caprock.  In a perfect system high capillary forces would prevent further vertical migration through the caprock.  However, in natural systems these caprocks may have fractures, faults or other higher permeability zones that result in leakage of the CO₂ into overlying formations.  If this leakage reaches shallow drinking water aquifers it presents a potential human health risk. 

The impact of CO₂ leakage on potential drinking water aquifers is currently unknown.  Thus, the amount of acceptable leakage cannot be quantified and potential risks cannot be taken into account during site selection.  Leakage of CO₂ into groundwater can result in lowering of the groundwater pH and increased dissolution of aquifer minerals thus increasing TDS, alkalinity or metal concentrations.  Success of geologic carbon sequestration relies, in part, on our ability to predict and quantify this potential degradation to groundwater quality.   Here we use reactive transport models to assess changes to groundwater quality as a result of CO₂ leakage.   Numerical simulations reacting common aquifer mineral and groundwater compositions with varying CO₂ leakage rates help identify parameters that indicate potential vulnerability in aquifers.