Effect of Fines Migration and Mineral Reactions on CO2 Injectivity and Relative Permeability

Fines migration and mineral reaction have been found to affect injectivity during CO2 sequestration in a sandstone aquifer. Previous laboratory studies measured single-phase permeability of sandstones before and after CO2 sequestration experiments to account for injectivity loss due to fines migration and mineral reactions. This thesis presents a series of experiments to investigate the link between fines migration & mineral reactions, and two-phase flow properties: wettability, injectivity and relative permeability. The experimental results are presented in Chapters 2 to 4. Chapter 2 presents the effect of wettability on fines migration during CO2 injection. The captive bubble method is used to measure contact angle of CO2-brine on Berea and Obernkirchener sandstones, and their mineral components: quartz, kaolinite, chlorite, microcline, and muscovite. All contact angles were measured under a pressure of 5.5MPa to 13.8 MPa at temperatures of 38°C and 55°C. The contact angle of the two types of sandstone indicates that their wettability was not clearly related to pressure and temperature. Quartz is found to be strong water-wet. Kaolinite, chlorite, and muscovite are found to be weak water-wet at 38°C, whereas microcline and muscovite show neutral-wettability at 55°C. SEM images reveal surface changes in kaolinite, chlorite, and muscovite after their exposure to CO2-saturated brine. For strong water-wet fines (contact angle < 30°), the maximum interfacial force remains relatively small and it increases with contact angle. So, minerals with greater contact angle are more prone to be mobilized with the interface. Therefore at 55°C, microcline and muscovite have more chance to be mobilized with CO2-brine interface than quartz, chlorite and kaolinite. Chapter 3 presents an analytical model to account for the capillary pressure boundary conditions during relative permeability estimation. The proposed model is validated using experimental data. The relative permeability functions generated using the proposed model yields a close match with the experimental observations. Chapter 4 examines the effect of fines migration and mineral reactions on CO2-water drainage relative permeability measurements, using a sintered glass core and six Berea sandstone cores. Three-stage and two-stage flooding are performed on the cores. Three-stage flooding involves injecting water, then CO2-saturated water, and finally water-saturated supercritical CO2. Two-stage flooding involves injection only of water and then water-saturated CO2, to avoid the chemical reactions brought about by CO2-saturated water injection and thereby reduce mineral reactions. Pressure difference across the cores and volumes of water produced are recorded. These data are used to generate CO2-water drainage relative permeability functions using the techniques developed in Chapter 3. For Berea cores, CO2 relative permeability is reduced (by 21% to 48%) during three-stage flooding when CO2-saturated water is injected. The reduction in CO2 relative permeability is found to be a function of pore volumes of CO2-saturated water injected. Experiments performed on the glass core suggest that the error in CO2 relative permeability caused by the absence of CO2-saturated water is negligible. Therefore, we propose that CO2-saturated water be omitted during CO2-water drainage relative permeability measurements