Hydrogen‐Brine‐Calcite Geochemical Interactions During Underground Hydrogen Storage

Underground hydrogen storage in porous geologic formations is a promising strategy to support the hydrogen economy by enabling large‐scale, seasonal energy storage. However, potential geochemical interactions between hydrogen and reservoir minerals, particularly calcite, remain poorly understood. This study uses a series of kinetic simulations to explore the interactions within a hydrogen‐brine‐calcite system using PHREEQC software. Various experimental studies from the literature were used to tune the models, including those on hydrogen solubility in brine and geochemical interactions with calcite. The findings indicate that using the default values of the PHREEQC dataset and the Van't Hoff equation to predict the equilibrium constant for the reaction associated with methane formation at high temperatures can be misleading, as these predictions incorrectly suggest increased calcite dissolution, hydrogen consumption, and methane production. To address this, a new temperature‐dependent analytical expression for the equilibrium constant for the mentioned reaction was developed, which was calibrated against the experimental observations. On the basis of this experimentally calibrated model, geochemical interactions in the hydrogen‐brine‐calcite system appear to be negligible at temperatures above approximately 70°C. Although on the basis of the results of a conceptual model with limited hydrogen availability, considerable hydrogen consumption due to geochemical reactions could occur at low temperatures (25–50°C), the overall hydrogen loss due to dissolution in the brine is generally far less than 1% (molar). This study offers insights into hydrogen‐brine‐calcite interactions and emphasizes the need for further experimental research.