Sealing potential of heterogeneous caprock in subsurface storage

Caprocks with inherently low permeability are crucial for ensuring long-term containment of injected fluids in subsurface geoenergy systems, particularly in the context of geologic carbon dioxide (CO2) and hydrogen (H2) storage. However, the integrity of these natural seals can be compromised by various multiphysical processes, including capillary breakthrough, hydraulic fracturing, chemical alteration, and stress-induced deformation. Lithological heterogeneity, as well as the presence of faults and fractures, further complicates the caprock sealing integrity under in-situ conditions. This dissertation investigates the sealing potential of three representative heterogeneous caprock formations: Eau Claire Shale and Maquoketa Shale from the Illinois Basin and Opalinus Clay from Switzerland. Through an integrated set of laboratory experiments that replicate subsurface stress and flow conditions, saturation states, and geochemical environments, a comprehensive experimental framework is established to characterize the caprock behavior. This framework includes measurements of CO2 breakthrough pressure, single- and multiphase permeability, saturated and unsaturated poroelastic parameters, time-dependent response, and coupled hydro-mechanical-chemical interactions. The study reveals that clay-rich facies within each formation consistently exhibit more favorable sealing performance compared to their sand-rich counterparts. These differences are attributed to variations in pore structure, mineralogical composition, and fabric anisotropy, which collectively influence fluid retention and deformation behavior. A key focus of this work is the evolution of the sealing properties post-CO2 breakthrough that could lead to changes in the hydromechanical response due to different fluid compositions and capillary responses. Furthermore, geochemical interactions, such as carbonate mineral dissolution, are demonstrated to substantially alter the caprock porosity over the duration of CO2 treatment. These time-dependent responses are assessed using a modified hydrostatic compression system, facilitating direct observations of the interplay between the mechanical compaction and chemical degradation. A coupled hydro-mechanical-chemical model is adopted and calibrated against the experimental outcomes to predict porosity evolution as a function of treatment time, pore structure characteristics, and mineral composition. Insights from an in-situ project titled CO2 Long-term Periodic Injection Experiment (CO2LPIE) are presented to evaluate the scalability of laboratory-derived parameters. Laboratory-scale experimental protocols are critically evaluated and adapted for integration with in-situ observations, providing a validated upscaling approach that bridges the gap between the core-scale tests and practical application in geologic CO2 storage. Finally, the developed framework is extended to assess the transport and capillary responses of heterogeneous rock under water-H2 system, pertinent to the emerging domain of underground hydrogen storage. Experiments elucidate the influence of thin shale interbeds and clay particle alignment on the capillary response, relative permeability hysteresis, and fluid trapping mechanisms, particularly in the bedding-normal direction. Overall, this dissertation presents a rigorous and versatile methodology for evaluating the sealing integrity of heterogeneous caprock and intraformational shale barriers under hydromechanical loading and chemical treatment. Its findings provide critical insights for site selection, risk assessment, and long-term monitoring strategies that support safe and effective subsurface storage.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Civil Engineering

Grantor

University of Illinois Urbana-Champaign

Year dc:date

2025

Author dc:creator

• Kim, Hyunbin

Contributors dc:contributor

• Makhnenko, Roman Y.
• Makhnenko, Roman Y
• Valocchi, Albert J
• Olson, Scott M
• Yan, Jinhui
• Willette, Donna C.

• Shale
• Co2 Storage
• Two-phase Flow
• Multiphysical Process
• Unsaturated Behavior
• Poroelasticity

Statement dc:rights

• Copyright 2025 Hyunbin Kim

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/130056

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F130056