Overview of the behavior of natural H2 in the subsurface and the H2-QUEST project

Natural hydrogen present in the subsurface is highly reactive, but a better understanding of the behavior of this molecule is important for developing to successful exploration models. The aim of this contribution is to present the state-state-of-the-art geochemical and microbiological processes that primarily consume natural hydrogen during its migration through the subsurface, and its retention while stored in the reservoir. Our approach combines published information with results from ongoing and past projects. In particular, we aim to investigate how pressure and temperature conditions control the different phase of hydrogen during migration and retention (hydrogen as free gas, microbubbles or dissolved in water). We will further examine how hydrogen's phase influences its reactivity with water and the surrounding rocks, affecting reaction rates and hydrogen consumption. In addition, we present the preliminary results from theoretical calculations of microbial consumption processes occurring at deep surface reservoirs using available data on cell numbers, metabolisms and reaction rates from hydrogen underground storage projects. The values will enable realistic and worst-case scenario of hydrogen consumption, which can be included in hydrogen reservoir stability assessments. The outcomes of this study will serve as constrains for follow up numerical models of natural hydrogen systems within the project H2-QUEST under the Joint Undertaking of the Clean Hydrogen Partnership.