Impact of Geochemical Reactions for Under-Ground Storage of Hydrogen Versus Ammonia

Abstract Challenges associated with Underground hydrogen storage (UHS), particularly those related to hydrogen's low density, high diffusivity, and the risk it poses on embrittlement of pipes, motivates consideration of ammonia as an energy carrier. This is because ammonia (NH3) is more compatible with pipeline materials and has a long history of industrial use with established regulations. Moreover, NH3 delivers energy at higher density compared to hydrogen (H2). All these benefits of ammonia can help speed up H2 transition for clean energy. This paper focuses on subsurface storage of H2 and NH3 as energy carriers. Both H2 and NH3 are reactive fluids. It is crucial to model and understand the impact of geochemical reactions that may occur in underground environments at elevated pressures and temperatures. This study introduces a holistic approach to model reactive transport phenomena linked to hydrogen loss under geologic conditions. First, geochemical simulations with kinetics related to hydrogen loss in the subsurface are conducted. The results of both static and dynamic equilibrium reactions are then integrated into a multi-phase reactive transport flow simulator, providing a comprehensive simulation of hydrogen loss under realistic injection, storage, and production scenarios. A homogeneous fully saturated aquifer with realistic mineralogical, petrophysical and fluid properties is assumed. Results indicate that sulfur (S) and iron(III) reduction are primarily responsible for the loss of H2 gas in the subsurface environment. Clay and silicate minerals exhibit minimal reactivity with H2 gas, suggesting that saline aquifers could be viable for hydrogen storage. Results also show that NH3 storage case demonstrates reduced geochemical reactions, promoting its significance in UHS. This builds up the case for NH3 as an alternate hydrogen carrier, considering the other perspectives of energy content, transportation cost, physical trapping efficiency, and operational safety. This study provides valuable insights into the behavior of both H2 and NH3 in saline aquifers, advancing the field of safe and efficient underground hydrogen storage for large-scale energy applications.