X-ray micro-computed tomography-based approach to estimate the upper limit of natural H 2 generation by Fe 2+ oxidation in the intracratonic lithologies

Natural hydrogen (H 2 ) emanations in intracratonic areas offer potentially exploitable carbon-free energy. To date, H 2 seepages have been detected in more than sixty sites with exploration ongoing in many locations. One mechanism of natural hydrogen generation is the oxidation of Fe 2+ in Fe-rich lithologies, and estimating the potential for hydrogen generation by this pathway is an important aspect of characterizing H 2 -generating rocks. However, accurate estimation of Fe 2+ can be challenging due to large-scale heterogeneities and small sample sizes used in conventional analysis. Here, we propose a correlative imaging technique to assess H 2 generation potential in Fe 2+ -rich source rocks by integrating 2D chemical information with 3D volumes of the rock imaged using X-ray computed tomography (micro-CT). The advantage of this method lies in its ability to analyze a whole drill core of the source rock to obtain the most representative values while preserving sample integrity. Our method, validated on fractured monzo-diorite from a natural H 2 -emitting well in Kansas, USA, yields an estimate of 707.93 ± 49.18 mol (H 2 )/ton (source rock), as the upper limit. The proposed method could be useful in characterizing source rocks and estimating their natural H 2 generation potential in the early stages of natural H 2 exploration.