Abstract
Underground hydrogen storage (UHS) in geological formations is a promising solution for large-scale, long-term energy storage, but its success depends on the integrity of the caprock seals. This study investigates how hydrogen (H2) exposure affects the geochemical and geomechanical responses of four potentially sealing shales (Tumey, Kreyenhagen, Santos, and Wolfcamp shales), selected for their varied mineralogy, lithology, and organic content. Shale samples were exposed for 30 days to H2-saturated brine under high-pressure, high-temperature conditions in a batch reactor. Samples were characterized before and after exposure to H2 using scanning electron microscopy (SEM), X-ray fluorescence (XRF) and X-ray diffraction (XRD), along with ultrasonic velocity measurements to assess changes in dynamic elastic properties. SEM revealed minor surface alterations, including localized calcite dissolution in Kreyenhagen and Santos shales and minor surface cracking in Tumey shale. After H2-brine exposure, dynamic Young's modulus decreased by 16.6 % (Tumey), 9.0 % (Kreyenhagen), 15.5 % (Santos), and 3.1 % (Wolfcamp). However, argon-brine control experiments showed equal or greater reductions in Young's modulus of 26.9 % (Tumey), 13.1 % (Kreyenhagen), 5.6 % (Santos), and 6.0 % (Wolfcamp). These results indicate that the H2-induced geomechanical weakening is minimal, and that brine-rock disequilibrium, not hydrogen reactivity is the primary driver of observed changes. These findings also suggest that H2 does not significantly compromise caprock mechanical integrity under the tested conditions. This study supports the viability of using shales with a range of organic content as effective caprock seals for UHS and provides critical insight for assessing the long-term safety of such storage sites.
| Original language | English |
|---|---|
| Article number | 150706 |
| Journal | International Journal of Hydrogen Energy |
| Volume | 161 |
| DOIs | |
| State | Published - Aug 22 2025 |
| Externally published | Yes |
Funding
This work was supported by Los Alamos National Laboratory's Laboratory Directed Research and Development – Directed Research program under LDRD-20230022DR. Los Alamos National Laboratory is operated by Triad National Security, LLC, for the National Nuclear Security Administration of the U.S. Department of Energy (Contract No. 89233218CNA000001). The unlimited public release number for this manuscript is LA-UR-25-22790. We are also thankful to our colleagues at the Material Science and Technology division in Los Alamos National Laboratory for enabling us to use their advanced high-resolution Scanning Electron Microscopy with Energy-Dispersive X-ray Spectroscopy.