MOLECULAR MODELING OF H2 AND CO2 INTERACTIONS WITH SHALE CAPROCKS

Abstract

The transition to a hydrogen-based energy economy and the global imperative for carbon neutrality necessitate the development of reliable, large-scale subsurface storage systems for hydrogen (H2) and carbon dioxide (CO2). This dissertation investigates the fundamental interactions of H2 and CO2 with shale caprocks, particularly clay-rich formations, using molecular dynamics (MD) simulations. The study focuses on three key aspects: (1) adsorption behavior of H2 and associated cushion gases (CO2 and CH4) on inorganic and organic surfaces under varying brine salinities; (2) multicomponent gas diffusion through nanoporous caprock systems; and (3) geochemical reactivity of H2 and CO2 with clay minerals, especially montmorillonite, under reservoir conditions.Results show that H2 exhibits weak adsorption on both clay and organic surfaces, with minimal loss to caprock via adsorption. In contrast, CO2 demonstrates strong affinity for organic matter and moderate interaction with clay minerals, suggesting its potential for both sequestration and as a cushion gas. Diffusivity analyses reveal that H2 transport is only marginally faster than CH4 and CO2, with values on the order of 10-7 m2/s, and that brine salinity has limited impact on gas mobility. Reactive MD simulations highlight that CO2 and H2 can induce structural deformation in clays under dry conditions, potentially compromising caprock integrity. However, water saturation mitigates these effects, preserving structural stability. This work provides molecular-scale insights into the storage behavior of H2 and CO2 in shale formations, offering critical guidance for the design and risk assessment of geological storage systems. The findings underscore the importance of mineralogy, fluid composition, and water content in governing storage performance and long-term containment.