Étude de l’impact de nouveaux gaz enrichis en hydrogène ou oxygène dans les stockages en aquifères

In many countries, a significant proportion of gaseous energy (natural gas) is stored underground in three main types of geological reservoirs: salt caverns, depleted reservoirs, and deep aquifers. In France, most geological reservoirs are located in deep aquifers, strictly anoxic underground geological formations constituted of porous rock containing water. In the coming years, changes in the energy mix will likely lead to the increased use of renewable gases like biomethane and dihydrogen (H2). Biomethane is similar to the currently stored natural gas. The main difference between these two gases lies in their dioxygen (O2) concentrations, as biomethane can be treated with this gas to remove the sulfide it may contain. This PhD thesis is part of the RINGS project, which focuses on the injection of new gases (O2 and H2) into deep aquifer storage.In this manuscript, the study focuses on the co-injection of H2 into natural gas. In addition to the increased risk of H2 migration due to its volatility, this molecule can serve as an energy source for many microorganisms present in deep aquifers. This microbial consumption, in addition to representing a loss of stored energy and a reduction in storage pressure, can lead to the production of methane (methanogenesis), acetate (acetogenesis), formate, or even sulfide (sulfate-reducers). However, the fate of H2 in deep aquifers remains largely unexplored. The difficulty of this study lies in the complexity of these environments from a physicochemical, mineralogical, and microbial point of view.In a previous PhD thesis, a collaborative, multidisciplinary approach involving imaging, analytical chemistry, mineralogy, microbiology, and process engineering was used to experimentally simulate the injection of 10% H2 into a UGS aquifer in a high-pressure reactor. However, the variability of the water and rock composition and microbial populations leads to variations in the observed phenomena.In the context of this PhD thesis, this approach has been improved and applied to four other French aquifers.This manuscript is divided into six chapters.•The first two chapters are devoted to the bibliography and the description of the material and methods.•The third chapter, presented as an article published in 2024 in the ‘International Journal of Hydrogen Energy,’ addresses the dependence of H2 storage viability on the site studied. This chapter compares the results of two new H2 co-injection simulation experiments applied to two storages with a previously conducted experiment using the same protocol. Extent of reaction equations were solved to identify and quantify the effect of different microbial metabolisms.•In the fourth chapter, the results of an experimental simulation of H2 co-injection into an aquifer with notably low salinity and low sulfate ion concentration are presented in the form of an article published in 2024 in the journal ‘Frontiers in Microbiology’. A protocol for calculating pH and redox potential, developed as part of this thesis work, is applied to this test and presented in this chapter.•In the fifth chapter, presented as a scientific article, the experimental protocol developed previously is applied to a new aquifer. The modeling of the experimental results by a kinetic model developed during this thesis work is presented in this chapter.•The general conclusion of this thesis work and the outlook are presented in the final chapter.•The experimental simulation of the injection of 100 ppm O2 into a matrix representing natural gas is presented in the appendix.