Salinity Effects on H₂S Generation in Subsurface Hydrogen Storage

In recent years, there has been a notable increase in the contribution of renewable energy to the overall supply of electrical energy. Nevertheless, the renewable energy sector encounters challenges in effectively storing surplus energy, particularly given fluctuations in energy demand driven by seasonal variations. As hydrocarbon reservoirs continue to deplete, storing hydrogen in subsurface formations has emerged as a promising solution to this dilemma. This study investigates the implications of sulfate-reduction reactions on hydrogen sulfide (H₂S) production within underground hydrogen storage reservoirs. Simulation results demonstrate significant H₂S generation during withdrawal cycles, posing challenges for hydrogen recovery and utilization. Factors influencing H₂S production include reaction kinetics, sulfate concentration, reservoir pressure, temperature, and formation water pH. H₂S exhibits preferential flow within higher-permeability layers and tends to accumulate in lower reservoir regions. Mitigation strategies, such as perforation techniques targeting upper sand portions, are recommended to reduce H₂S production. Our findings suggest that reservoirs with substantial sulfate content may not be optimal for underground hydrogen storage initiatives. Sensitivity analyses indicate a correlation between sulfate concentration and prolonged H₂S production until sulfate depletion. However, uncertainties persist regarding continuous aqueous sulfate diffusion from formation rocks. Despite potential hydrogen losses due to methanogenation and sulfate reduction, further validation through field applications is needed. This study underscores the importance of considering H₂S production in underground hydrogen storage planning and highlights the need for mitigation measures to ensure safe and efficient operations.