Committee Members Information

• Ph.D. Advisor Name: Hussein Hoteit
• External Examiner Name: Abbas Firoozabadi
• Committee Chair Name: William Roberts
• 4th Committee Member Name: Abdulkader Alafifi

Abstract

Geologic carbon sequestration (GCS) has been identified as a promising solution to help mitigate rapidly rising atmospheric CO₂ concentrations. Subsurface carbon mineralization, whereby CO₂ reacts with divalent cations liberated due to rock dissolution to form stable carbonate minerals, is considered one of the safest GCS methods. This dissertation studies carbon mineralization in basalts and investigates key underlying and consequential phenomena of this process. It explores reaction kinetics, controls on flow and transport, and potential environmental impacts of GCS in basalts. This is done through a diverse set of complementary tools, including: lab-scale experiments, advanced imaging and characterization techniques, geochemical modeling, high-fidelity simulations, and applied machine learning.

The first part of this dissertation is related to the Jizan carbon mineralization pilot in Western Saudi Arabia. The Jizan pilot is the second of its kind globally, injecting 131 tons of water-dissolved CO₂ into the Jizan Group basalt for carbon mineralization. We investigate the mineral carbonation potential of the Jizan basalt, presenting for the first time direct evidence of mineralization. Next, we study the dissolution kinetics of the Jizan basalt, providing important insights into its dissolution behavior and key kinetic data for geochemical and reactive transport modeling. In addition, we investigate the mobilization of trace and toxic elements into the groundwater due to basalt dissolution. Results show limited trace element mobility, highlighting the minimized risk of groundwater contamination.

The second part of this dissertation studies flow and transport in fractures. Basalts inherently have very low matrix permeability and generally depend on fracture networks for flow and transport. We investigate the effect of fracture roughness on hydraulic properties in basalts through core flooding experiments. Results show the profound effect of roughness with up to 50% reduction in effective flow in highly rough fractures. Finally, we develop a deep-learning model for predicting hydraulic properties of complex fractures from image data. Our model shows high prediction accuracy and computational efficiency, outperforming traditional cubic-law-based models.

Overall, this dissertation presents an integrated understanding of carbon mineralization in fractured basaltic systems, providing key insights into dissolution and precipitation kinetics, trace element mobility, and flow and transport in fractures.