Insights into reaction mechanisms: Water’s role in enhancing in-situ hydrogen production from methane conversion in sandstone

Abstract

In-situ conversion of subsurface hydrocarbons via electromagnetic (EM) heating has emerged as a promising technology for producing carbon-zero and affordable hydrogen (H₂) directly from natural gas reservoirs. However, the reaction pathways and role of water as an additional hydrogen donor in EM-assisted methane-to-hydrogen (CH₄-to-H₂) conversion are poorly understood. Herein, we employ a combination of lab-scale EM-heating experiments and reaction modeling analyses to unravel reaction pathways and elucidate water’s role in enhancing hydrogen production. The labelled hydrogen isotope of deuterium oxide (D₂O) is used to trace the sources of hydrogen. The results show that water significantly boosts hydrogen yield via coke gasification at around 400 °C and steam methane reforming (SMR) reaction at over 600 °C in the presence of sandstone. Water-gas shift reaction exhibits a minor impact on this enhancement. Reaction mechanism analyses reveal that the involvement of water can initiate auto-catalytic loop reactions with methane, which not only generates extra hydrogen but also produces OH radicals that enhance the reactants’ reactivity. This work provides crucial insights into the reaction mechanisms involved in water-carbon-methane interactions and underscores water’s potential as a hydrogen donor for in-situ hydrogen production from natural gas reservoirs. It also addresses the challenges related to carbon deposition and in-situ catalyst regeneration during EM heating, thus derisking this technology and laying a foundation for future pilots.