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 (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 Fe2+ 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 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 H 2 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 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. • We propose a method to quantify Fe2+ in a H 2 source rock by an imaging technique. • Upper limit of H 2 generation in mols (H 2)/ton (rock) was obtained assuming that all Fe2+ reacted to generate H 2. • Method allows imaging large representative samples such as drill cores (1 m). • Ensures minimal sample destruction and high accuracy. [ABSTRACT FROM AUTHOR]