Natural hydrogen exploration: A case study of hydrogen wells in the Mali gas field in Africa and global advances

This study aims to enhance the exploration and exploitation of China's natural hydrogen reservoirs and to advance research on the distribution, enrichment mechanisms, and accumulation conditions of natural hydrogen. Based on a literature review, we perform a case study of natural hydrogen exploration in the Mali hydrogen field within the Taoudeni Basin in Africa and introduce global advances in natural hydrogen exploration. The results reveal that the hydrogen in the Mali gas field most likely originates from the active serpentinization of 2.2-2.1 Ga rocks in the Leo-Man Shield of the West African Craton and, thus, is the product of reactions of ferrous irons in rocks with water. The Mali hydrogen field contains two distinct types of reservoirs, namely the upper dolomitic carbonate reservoir and the lower sandstone reservoir, where free hydrogen and dissolved hydrogen are primarily found, respectively. Hydrogen migrates from the source to these reservoirs primarily along faults, subsequently accumulating beneath diabase cap rocks. Increasingly more companies have engaged in natural hydrogen exploration worldwide, with their number surging from three in 2020 to 40 in 2023, and multiple countries have started to issue hydrogen exploration licenses. Nevertheless, the exploration and production of natural hydrogen are still in their initial stages, with only a few successful cases. Therefore, greater efforts are necessary to conduct scientific exploration and achieve technological breakthroughs.