Numerical Evaluation of Viscous Fingering Behavior During Underground Hydrogen Storage in Saline Aquifers

ABSTRACT: Underground hydrogen storage (UHS) is a promising option for fully realizing hydrogen potential as an alternative energy source to balance seasonal availability with irregular demand. This study is motivated to investigate and evaluate the viscous fingering behavior during underground hydrogen storage. The specific numerical simulations are implemented using a component simulator, incorporating input parameters such as density, viscosity, salinity, and relative permeability curves, all derived from experimental data. The study findings are first validated through a comparison with oil-water two-phase lab-based flat-plate displacement experiments. Numerical simulation schemes with different grid sizes are employed for comparison with experimental results, validating and optimizing the grid independence to determine the optimum fine grid size. Utilizing the same physical model, a hydrogen-aquifer water two-phase system is subsequently adopted to study the phenomenon of viscous fingering during the hydrogen injection process. The results show that in general, for the studied cases, there is no significant difference between the two mesh sizes, especially in the water recovery factor and hydrogen mass ratio. Based on the current numerical model and results, fingering behavior has a relatively minor impact on the underground hydrogen storage process. 1. INTRODUCTION As the global climate crisis intensifies, transitioning to a low-carbon economy has become an urgent global mission (Zhao, Jia 2023, He, Liu 2024, Wang, Liu 2024). To reach such an ambitious target, a multitude of solutions are being explored and developed. Hydrogen, as a clean energy carrier, has garnered widespread attention (Zhang, Jia 2024, Bai, Jia 2024). Hydrogen not only possesses various advantages, such as high energy density and zero emissions, but it also plays a significant role in supporting renewable energy systems. When there is an overproduction of renewable energy, hydrogen can be produced through the electrolysis of water, thus forming a closed-loop system for a low-carbon transition. However, the application of hydrogen currently encounters a series of challenges, particularly with the storage of hydrogen. The interaction between hydrogen and metal ions, for example, can cause hydrogen embrittlement. In response, underground hydrogen storage technology has been developed. Utilizing the natural advantages of underground spaces, such as consistent environmental conditions, capacity for large-scale storage, and increased safety, the technology provides a promising approach to enable extensive, secure, and dependable storage of hydrogen.