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Microfluidic Investigations of CO2 Mass Transport at Elevated Pressure and Salt Precipitation

  • Author / Creator
    Ho, Tsai Hsing
  • Carbon capture and sequestration (CCS) in geological reservoirs is one of the mitigation strategies to slow down the increasing atmospheric CO2 concentration due to human activities. Effectively characterizing the transport phenomena between CO2 and materials in reservoirs, including mass/heat transfer and phase change, is crucial but challenging for accurately evaluating potential storage sites and monitoring the injection operation. This doctoral study conducts microfluidic experiments to elucidate the transport behaviors of CO2 and water at the injection pressure from 0.1 up to 9.5 MPa and the temperature between 22 and 35 ○C, corresponding to a deep injection depth. To this end, we develop a high-pressure microfluidic platform and operating procedures for high-pressure experiments. Three primary projects are carried out addressing the important issues of carbon storage engineering.

    Firstly (Chapter 3), we quantify the volumetric mass transfer coefficient (kLa) of CO2 at three different states (i.e., gas, liquid, and supercritical phase) to elucidate the pressure effect
    on the mass transfer process, by measuring the size change of CO2 micro-bubbles/droplets generated using a microfluidic T-junction. The results show a significantly enhanced mass transfer of supercritical CO2 in water, while the injection pressure has a minor influence on the kLa measured from gas and liquid CO2. kLa shows a positive correlation with the
    continuous phase’s Reynolds number, implying the importance of bubble/droplet speed on transporting CO2.

    Secondly (Chapter 4), we observe an intriguing multi-phase CO2 flow and emulsions when operating at the pressure-temperature (P -T) condition close to the CO2 gas-liquid phase boundary. We propose a series of strategies to unravel this complex multi-phase dynamics and quantify the CO2 mass transfer while changing its phase state. The resulting kLa decreases exponentially with time, which may be influenced by the shrinking specific area (a), CO2 concentration gradient in the water slug, and the slowing down CO2’s traveling speed.

    Thirdly (Chapter 5), we investigate the effects of pore-structures and brine concentrations on salt precipitation, which is a potential threat to hinder CCS in deep saline aquifers, using 2-D planar porous microfluidics. Three distinct stages are observed: (I) initial, (II) rapid growth, and (III) final phases, in the progression of salt nucleation with different rates and size distributions upon brine drying. The location of large brine pools plays an essential role in determining the distribution and size of nucleating salt. The positive correlation between the brine-drying and salt-precipitation speeds may help evaluate salt’s precipitation speed for different porosities.

    Finally (Chapter 6), research outlook and future projects are given, particularly regarding microfluidic applications and studies of carbon capture and sequestration technology in
    saline aquifers at elevated pressure conditions.

  • Subjects / Keywords
  • Graduation date
    Fall 2021
  • Type of Item
    Thesis
  • Degree
    Doctor of Philosophy
  • DOI
    https://doi.org/10.7939/r3-zy1m-kx79
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.