X-ray micro-computed tomography-based approach to estimate the upper limit of natural H2 generation by Fe2+oxidation in the intracratonic lithologies

Natural hydrogen (H2) emanations in intracratonic areas offer potentially exploitable carbon-free energy. To date, H2 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 Fe2+ in Fe-rich lithologies, and estimating the potential for hydrogen generation by this pathway is an important aspect of characterizing H2-generating rocks. However, accurate estimation of Fe2+ 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 H2 generation potential in Fe2+-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 H2-emitting well in Kansas, USA, yields an estimate of 707.93 +/- 49.18 mol (H2)/ton (source rock), as the upper limit. The proposed method could be useful in characterizing source rocks and estimating their natural H2 generation potential in the early stages of natural H2 exploration.