Will mercury impurities impact CO2injectivity in deep sedimentary formations? I. Condensation and net porosity reduction

Mercury is a common contaminant in natural gas and partially follows carbon dioxide through amine separation during natural gas processing. In this study, we used simple volumetric analyses, the simulator TOUGH2/EOS7C, and dew-point calculations to investigate the potential impacts on injectivity of trace amounts of mercury in a carbon dioxide stream injected for geologic carbon dioxide sequestration. For mercury concentrations up to 190 ppbV (∼1.6 mg/stdm3 CO2), the total volumetric pore-space plugging that could occur around the wellbore due to complete condensation of mercury, or due to complete precipitation of mercury as cinnabar, results in a very small porosity change. Evaporative concentration of aqueous mercury by water evaporation into carbon dioxide is unlikely because the volatility of mercury into the carbon dioxide stream is higher than that of water. Dew-point calculations suggest that mercury concentrations of about 2000 ppbV are needed for mercury condensation to occur. Our analyses suggest that for mercury concentrations of a few hundred ppbV, the impacts on injectivity of mercury deposition by condensation or precipitation as cinnabar are negligible.