Speaker
Description
Depleted shale reservoirs are regarded as promising sites for large-scale underground hydrogen storage due to their low cost, large capacity, and high recovery purity. However, during storage, geochemical and biochemical reactions involving the injected hydrogen can generate H2S—a contaminant that reduces gas purity during the production phase. Owing to atomic substitution, nanopores within shale clay minerals develop a self-generated electric field. Clarifying the interplay between this field and the retention of polar H2S, and uncovering the governing mechanisms, are critical for accurately predicting and mitigating its production—a pivotal area that remains unexplored. In this study, grand canonical Monte Carlo and molecular dynamics simulations were employed to compare the H2S retention capacities of illite, quartz, and kerogen in shale. We quantified the strength of the self-generated electric field in illite and elucidated how it enhances illite’s retention capability. Furthermore, we revealed, from a microscopic perspective, the distinct mechanisms by which pore size, water content, and salinity affect the self-generated electric field. The results indicate that, unlike quartz and kerogen, which can only adsorb a limited amount of H2S on pore walls, illite—through strong electrostatic interactions induced by its self-generated electric field—not only enhances H2S adsorption on pore surfaces but also effectively enriches a substantial amount of H2S in the central pore region via field-driven adsorption. In a 4 nm illite slit pore, the electric field intensity at the center reaches 9.67 V/nm, and the total H2S retention is 82.03 and 73.28 times greater than in quartz and kerogen, respectively. A pore size of 4 nm is identified as the critical threshold affecting the field intensity. Below this size, field strength diminishes primarily due to promoted migration of K⁺ from the ionic to the hydroxyl surface; above it, reduction is mainly caused by the increased distance between these two surfaces. The self-generated electric field also promotes the formation of water bridges, which act as ion channels that facilitate K+ migration and further reduce field intensity. Additionally, under the influence of this field, brine anions and cations separate to form a polarized electric field. High brine concentrations promote K+ migration, collectively diminishing the self-generated field strength. Therefore, during hydrogen storage in shale, the generated H2S is primarily retained in clay mineral nanopores around 4 nm in size, especially under conditions of low water content and low salinity. This study addresses the knowledge gap regarding the enhancement of H2S retention by clay mineral self-generated electric fields during depleted shale hydrogen storage and offers novel insights for the design of desulfurization systems.
Keywords: Underground hydrogen storage; H2S; Illite; Self-generated electric field; Shale; Molecular simulation.
| Country | China |
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