Geomechanical failure of underground hydrogen storage (UHS) systems.

Abstract

Green hydrogen gas produced from electrolysis of water using off-peak electricity from renewable sources is a clean energy source. Large-scale hydrogen production for energy generation will therefore help in achieving a significant reduction in greenhouse gas emissions and global net-zero targets. Underground Hydrogen Storage (UHS) in salt caverns, saline aquifers and depleted oil and gas reservoirs has recently been recognised as a critical enabling technology for the large-scale storage of hydrogen gas. However, the UHS system environment may be adversely affected by complex processes driven by fluid flow, geochemical and geomechanical phenomena and governed by evolutionary changes in the subsurface stress regime and the interactions between the pore fluids, formation rock minerals and the injected/stored hydrogen gas. In addition, injection of hydrogen gas into subsurface formations can cause over-pressurisation and induced seismicity which may lead to formation failure. In this work, we develop a hydro-chemo-mechanical model to determine formation failure potential in underground hydrogen gas storage systems. This model captures the complex combined processes of fluid flow, geochemistry and geomechanics. Analysis of the results, based on changes in the volumes of the constituent minerals in the formation and the Mohr-Coulomb failure criterion, shows significant changes in the porosity and permeability and some impact on the geomechanical integrity of the storage formation