Engineered subsurface hydrogen generation: Insights for sustainable production system

Abstract

Subsurface hydrogen generation encompasses both natural and engineered processes. Natural subsurface hydrogen, often referred to as geological hydrogen, is produced by in-situ geochemical reactions without human intervention. The term engineered subsurface hydrogen generation is adopted here to describe controllable reservoir operations aimed at producing hydrogen, which can be further divided into three routes, namely stimulated geological hydrogen via serpentinization of ultramafic rocks by water-looping, subsurface chemical looping via steel-slag-mediated iron redox water splitting, and subsurface conversion of organic-rich formations via thermal, biological, or chemical pathways. Only stimulated geological hydrogen falls within the strict definition of geological hydrogen; the other two are engineered subsurface processes that do not qualify as geological hydrogen. Our experiments on serpentinization indicate that hydrogen generation and release can be physically decoupled, implying that engineered production strategies such as pressure drawdown and cyclic injection-production are required. Crucially, the field value of engineered subsurface hydrogen generation depends on whether these hydrogen-generating reactions can be engineered as controllable reservoir operations. These routes therefore require reaction-specific production systems rather than a universal well pattern. Drawing on geothermal doublets, multistage-fractured horizontal wells, radial jet laterals, shock fracturing and blasting fracturing, a completion-centered framework is outlined in which wellbores, fractures, catalysts or reactive solids, renewable heating, hydrogen separation and underground storage are designed as one production system. Key questions are further identified, including reaction kinetics coupled with heat and mass transfer, catalyst and injectivity maintenance, and pilot evaluation by H₂ recovery, energy output-input ratio and carbon balance.

Document Type: Editorial

Cited as: Wang, B., Wang, H., Li, G., Zhu, X., Cheremisin, A., Yuan, C. Engineered subsurface hydrogen generation: Insights for sustainable production system. Advances in Geo-Energy Research, 2026, 21(3): 297-300. https://doi.org/10.46690/ager.2026.09.08