Energy, Environmental and Chemical Engineering
Date of Award
Doctor of Philosophy (PhD)
Chair and Committee
Geologic CO2 sequestration: GCS) is a promising approach to reduce anthropogenic CO2 emissions into the atmosphere. At GCS sites, injected CO2 is kept in formation rock by an overlying low permeability caprock. During and after CO2 injection, geochemical reactions can affect the porosity, permeability, and pollutant transport in aquifers. Despite their importance, nano- and micro-scale subsurface geochemical reactions are far from well-understood.
Clay mobilization has been reported to decrease aquifer permeability during water flooding, and clay minerals are abundant in caprock. Thus, we studied CO2-brine-clay interactions under varied conditions relevant to different GCS sites: at 35-95°C and under 35-120 atm CO2, in water, NaCl, MgCl2, or CaCl2 solutions). Biotite, Fe-bearing mica, was used as a model clay mineral. We observed numerous fibrous illite precipitates on mica after reaction for only 3 h, which had not been previously reported. A few hours later, the mica surface cracked and fibrous illite detached. The mobilization of fibrous illite can decrease the aquifer's permeability greatly and affect the safety and efficiency of GCS. Mechanisms related to ion exchange, mica swelling, and CO2 intercalation were explored. Oriented aggregation of illite nanoparticles forming the fibrous illite was directly observed, suggesting a new mechanism for fibrous illite formation. Interestingly, besides the pH effect, aqueous CO2 enhances mica cracking over N2. These findings can help to achieve safer subsurface operations.
At GCS field sites, Fe concentration increased near the injection sites and originally adsorbed pollutants were released. As the brine flows, Fe re-precipitated because of pH increase. To better predict the fate and transport of aqueous pollutants, the nucleation and growth of Fe(III): hydr)oxides were studied. New information about sizes and volumes of the Fe(III): hydr)oxide nanoparticles precipitated in solution and on quartz, mica, and sapphire were provided using small angle X-ray scattering, in the presence of different ions: Al3+, Cl-, NO3-, and SO42-). Using complementary techniques, the controlling mechanisms related to surface charge, bond formation, and interfacial energies were explored. These new findings can help better predict pollutant transport in aquifers not only at GCS sites, but also in managed aquifer recharge and acid mine drainage sites.
Hu, Yandi, "Roles of Nano- and Micro-Scale Subsurface Geochemical Reactions on Environmentally Sustainable Geologic CO2 Sequestration" (2013). All Theses and Dissertations (ETDs). 1136.