Evaluating Hydrogen Generation in Fractured Iron-Rich Rocks Under Dynamic Subsurface Conditions

Abstract This study investigates hydrogen generation from iron-rich ultramafic rocks under dynamic subsurface conditions, with a focus on the effects of fracture geometry, proppant support, and variations in flow rate. The goal is to evaluate how these factors influence hydrogen yield and reactive surface exposure. Coreflooding experiments were conducted on fractured ultramafic rock samples under 1800 psi confining pressure and controlled thermal conditions. Both propped and unpropped fractures were tested using brine injection at varying flow rates. Hydrogen production was monitored in real time using a Micro-GC, and effluent chemistry was analyzed via ICP-OES. Pre- and post-experiment CT scans were used to assess changes in fracture morphology and porosity. Propped samples exhibited higher permeability and greater hydrogen generation, demonstrating the critical role of fracture aperture in enhancing reactivity. Rate sensitivity tests revealed that higher flow rates led to more sustained hydrogen production, as analyzed using first-order decay kinetics. Iron content correlated strongly with hydrogen evolution, while magnesium remained stable, and calcium and aluminum showed limited variation. This work also introduces a novel method to quantify hydrogen mass across a fractured surface during serpentinization coreflooding, and provides unique insights by integrating gas monitoring, elemental analysis, and CT imaging, laying the foundation for more accurate modeling and optimization of hydrogen generation and recovery from ultramafic formations.