Roles of Nano- and Micro-Scale Subsurface Geochemical Reactions on Environmentally Sustainable Geologic CO2 Sequestration

<p>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.</p><p>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&deg;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.</p><p>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: Al<super>3+</super>, Cl<super>-</super>, NO₃<super>-</super>, and SO₄<super>2-</super>). 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.</p>

Name thesis:degree_name

Doctor of Philosophy (PhD)

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Energy, Environmental and Chemical Engineering

Year dc:date.available

2013

Author dc:creator

• Hu, Yandi

Contributors dc:contributor

• Young-Shin Jun

Language dc:language

English (en)

DOI

https://doi.org/10.7936/K73776S1

OAI identifier oai:identifier

oai:openscholarship.wustl.edu:etd-2136