Using 3D Tomography to Understand Fluid-Fluid Interface Evolution in Porous Media for Carbon Sequestration Applications
Fundamental understanding of multi-phase flow in porous media is needed to deploy subsurface engineering processes such as geologic carbon sequestration (GCS) that works by injecting and storing carbon dioxide (CO2) into underground geologic formations. In this PhD project, the in-situ fluid configuration was visualized within the opaque porous media with the utilization of X-ray micro-tomographic (MCT) imaging for multiple fluid-fluid-solid systems at physical scale of micrometer. With further image processing, qualitative and quantitative analyses were performed on the acquired MCT data for a total of three sets of experiment. In the first set of experiment, we investigated the representative elementary volume (REV) for a set of fundamental physical parameter measurements such as porosity and specific interfacial area; and topological measures including Betti numbers and the corresponding Euler characteristic that are relevant to fluid connectivity for an air-water-sandstone system under ambient conditions. We aimed to investigate the effect of the saturation level of water and image resolution on the REV of the parameters investigated. We observed that both the saturation level and the image resolution affects the REV of the parameters of interest. Moreover, we conclude that for connectivity results applicable to flow processes in macropores, treatment of microporosity presented mainly in clays is necessary. The second set of experiment aimed to investigate the interphase mass transfer process of supercritical CO2 (scCO2) into brine for a scCO2-brine-sandstone system under experimental conditions relevant to GCS. Throughout the experiment during which brine was injected continuously to dissolve any trapped scCO2 clusters in pore space, time-evolution of the scCO2 clusters were tracked by implementing a cluster-matching workflow. The mass transfer coefficient was then calculated for each completely depleted scCO2 cluster, and were averaged for the entire system as a bulk mass transfer coefficient, with which we back-calculated the three-dimensional (3D) in-situ CO2 concentration fields. It is expected that the mass transfer coefficients calculated in this study might serve as reference values for the application of GCS, and we expect the methodology presented for calculating the mass transfer coefficients to be applied to other relevant experimental works. Lastly, we investigated the effect of core heterogeneity and miscibility on the invasion patterns of scCO2 for scCO2-brine-sandstone systems under experimental conditions relevant to GCS. The experiments were carried out with two sandstone cores with transverse layered core-scale heterogeneity under both partially miscible and immiscible conditions, and the 3D dynamic invasion patterns of scCO2 were tracked continuously throughout the experiments with MCT. Our results demonstrate that when the layered heterogeneity was minor, flow patterns of scCO2 were similar under partially miscible and immiscible conditions, and scCO2 saturation profiles eventually converged. However, flow patterns of scCO2 were very different with slightly higher layered heterogeneity, and scCO2 saturation did not converge after injection of 10s pore volume (PV) of scCO2. These observations indicate that flow patterns of scCO2 are sensitive to the minor changes in miscibility during the initial stage of the experiments when coupled with mild level of core heterogeneity. Overall, the methodology and results presented in this thesis would contribute to the application of GCS; and many other relevant subsurface engineering processes such as underground hydrogen storage, enhanced oil recovery, and water remediation of non-aqueous phase liquids. The results presented herein would also benefit the broad topic of multi-phase fluid flow in porous media.
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