Evaluating Geological Seals for Underground Hydrogen Storage: A Comprehensive Assessment

Abstract

ABSTRACT: Underground Hydrogen Storage in porous media offers a viable solution for long-term, large-scale energy storage. Yet, challenges such as low storage efficiencies and potential losses persist, with a key issue being the sealing capacity and integrity of the storage reservoir. This study specifically addresses two primary hydrogen leakage mechanisms in caprocks: capillary leakage and faults or fractures in the caprock. We conducted static reactivity tests on various shale samples, at a constant pressure of 3.4 MPa and exposed to hydrogen in the presence of brine under different temperature conditions over 30-day periods. The findings generally indicate low reactivity of hydrogen with the shale samples. Minor compositional changes were observed, which were determined through XRD analysis. However, significant alterations in petrophysical properties were observed in all the plug samples, including more than a 100% increment in porosity and even greater changes in permeability. Additionally, uniaxial compressive strength tests were conducted, revealing that the shales exhibited a reduction in all mechanical properties. Micro-CT scans confirmed the increases in permeability and exposed the presence of small microcracks. These findings underscore the potential for hydrogen storage to modify shale structure by reopening microcracks, emphasizing the need for further research to fully understand the geochemical interactions at play. 1. INTRODUCTION The urgency of transitioning to a clean, low-carbon energy future underscores the pivotal role of energy storage technologies. These technologies are crucial for integrating intermittent renewable energy sources, such as wind and solar, into the electrical grid to ensure a consistent energy supply. Particularly, large-scale energy storage is instrumental in facilitating the shift towards more sustainable energy systems, a topic that has gained prominence in recent research (Krevor et al., 2023). A primary challenge in the renewable energy sector is the mismatch between the periods of energy production and peak demand times (Matos et al., 2019), as depicted in Figure 1. This discrepancy underscores the critical need for efficient energy storage solutions that can store excess energy during high production periods and release it during peak demand times. The transition towards renewable energy sources amplifies the urgency for such solutions to combat climate change.