Hydrogen sulfide in underground hydrogen storage sites: Implication of thermochemical sulfate reduction

Abstract

Hydrogen is recognized as a clean energy carrier that can decarbonize heavy industry and the aviation system. However, the infrastructure is not yet ready for a hydrogen economy and large-scale hydrogen storage is needed to balance the mismatch between supply and demand. Therefore, depleted gas fields have been proposed as suitable storage sites, given the presence of infrastructure and pipeline network for distribution and utilization. Attempts have been made to analyze the suitability of these reservoirs for hydrogen storage, with a focus on choosing higher temperature and salinity conditions to neutralize the effects of microbial activities as one of the main sources of hydrogen loss in the depleted gas reservoirs. However, thermochemical sulfate reduction (TSR) is activated at high temperatures and has a huge potential not only to consume hydrogen through abiotic reactions but also to generate a huge amount of (Formula presented.). In this study, a one-dimensional diffusion-based mass transport model was built using PHREEQC to highlight the potential challenges posed by the TSR in depleted gas fields. The results obtained indicated that the presence of iron minerals (pyrite and hematite) is crucial for (Formula presented.) generation through TSR reactions. An increase in temperature also leads to an increase in (Formula presented.) concentration in the brine and gas phase. However, since most of the (Formula presented.) formation comes from pyrite dissolution and pyrite dissolution is still strong at lower temperatures, a low temperature is not necessarily the best selection criterion to avoid (Formula presented.) formation. Thus, precautions must be taken to ensure that activation of TSR does not pose significant environmental problems.