Mitigating Global Warming with Underground Hydrogen Storage: Impacts of H2S Generation

Summary In the last few years, the share of renewable energy as a supply source for electrical energy has increased. However, the renewable energy sector is faced with the problem of storing the excess energy produced due to fluctuation of energy demand due to seasonality. Storing hydrogen in subsurface formation has become a viable option in recent years as more hydrocarbon reservoirs are depleted. A review of the literature revealed that there are limited modelling efforts for underground hydrogen storage in depleted gas reservoirs owing to a lack of field implementation for calibration. Modelling of such processes is important for operators to be able to design as Underground Hydrogen Storage (UHS) properly for HSE reasons especially considering some reservoirs may be prone to reservoir souring due to biochemical reactions with hydrogen injection. The simulation model used in this study and simulation cases were run using Eclipse to evaluate the magnitude of hydrogen losses due to sulfate-reduction reactions. In addition, H2S generation from this reaction will also be evaluated to see the potential impact on overall UHS operations. Furthermore, the H2S quantity will be limited by the available amount of CO₂, thus, the solubility of CO₂ in the formation water will be highlighted. From this modelling study, it is observed that depending on the estimated reaction rate and sulfate concentration, H2S generated and produced can be of considerable amount which can pose serious HSE problems. It also means that less hydrogen will be recovered for power generation because some hydrogen will be converted to CO₂ and H2S in the reservoir, rendering UHS uneconomical and not a viable option for hydrogen storage. Selection of depleted hydrocarbon reservoirs for UHS must then take into account rock minerals, formation water pH, reservoir pressure and temperature among others to ensure maximum hydrogen is recovered.