Understanding caprock integrity in underground hydrogen storage: A geochemical study of mineral alteration and sealing efficiency
本文聚焦于地下含水层储氢（UHS）系统中盖层的完整性问题。盖层作为阻止氢气向上迁移的关键屏障，其密封性能直接影响储氢系统的安全性与长期稳定性。尽管已有大量研究关注储层内的地球化学反应，但氢气与盖层矿物之间的相互作用及其对盖层封盖性能的影响仍缺乏系统研究。
本研究通过数值模拟方法，系统评估了pH值、温度、压力和盐度等关键参数对盖层孔隙度、渗透率及封盖能力的影响。结果表明，氢气与方解石、白云石等矿物的反应会显著改变盖层的物理化学性质。在酸性条件下，矿物沉淀导致孔隙度下降超过0.05%；而在碱性条件下，孔隙度略有上升。高温会加速地球化学反应，增强孔隙度变化；压力则对反应方向起关键作用，低压促进矿物溶解、增加孔隙度，从而提高泄漏风险；高压则抑制反应，增强封盖性能。此外，高盐度环境促进岩盐沉淀，使孔隙度降低0.2%，有效提升盖层密封性。
本研究为UHS项目中盖层稳定性管理提供了量化依据，强调了优化地球化学条件以减少氢气泄漏风险的重要性。
CMG软件应用情况
本研究采用CMG-GEM（Computer Modeling Group Ltd. 开发的多相组分模拟器）进行数值模拟。该软件具备模拟多孔介质中流体流动及流体-岩石间地球化学反应的能力，特别适用于地下储氢系统中复杂的物理-化学过程模拟。模型参数经过多次优化，确保模拟结果准确反映不同地质和地球化学条件下盖层的响应行为。
研究结论
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- 盖层完整性是地下储氢系统安全性的关键保障；
- 氢气与盖层矿物（如方解石、白云石）之间的地球化学反应会显著改变盖层的孔隙度和渗透率；
- 泄漏风险主要受毛细压力和分子扩散控制，模拟结果显示基础模型中氢气泄漏率超过行业标准1%；
- 高温、低压和酸性环境会加剧盖层矿物溶解，增加泄漏风险；
- 高盐度和高压条件有助于矿物沉淀，增强盖层密封性；
- 优化储氢环境的地球化学参数对于提升盖层稳定性和减少氢气泄漏至关重要。
Abstract
Underground hydrogen storage (UHS) in aquifers has emerged as a promising large-scale energy storage solution, crucial for enabling the transition to renewable energy systems. Ensuring the safety and long-term reliability of UHS is essential to support increased adoption and integration of renewable energy sources into existing energy infrastructures. However, the success of UHS systems depends not only on effective management of the physical properties of reservoirs but also on a comprehensive understanding of the geochemical interactions between hydrogen and the surrounding rock formations, especially the caprock. While existing literature predominantly addresses geochemical reactions within the reservoir, research focusing on hydrogen-induced a b a b c Share Citemineral alteration that may affect caprock integrity remains limited. This study aims to bridge this critical gap by investigating the geochemical interactions between hydrogen and caprock minerals and their subsequent impact on caprock integrity and hydrogen leakage potential. Numerical simulations were performed to assess the effects of varying pH, temperature, pressure, and salinity on the porosity, permeability, and sealing capacity of the caprock. The results reveal that hydrogen interactions with key minerals, such as calcite and dolomite, induce significant alterations in the physical and chemical properties of the caprock, potentially compromising its sealing effectiveness. Under acidic conditions, mineral precipitation leads to a reduction in caprock porosity over 0.05 %, whereas under alkaline conditions, a slight increase in porosity is observed. Elevated temperatures further accelerate geochemical reactions, intensifying the changes in porosity. Pressure significantly influences geochemical processes with lower pressures facilitating mineral dissolution and increasing porosity, which increases leakage risk. In contrast, higher pressures suppress geochemical reactions, enhancing the caprock’s sealing integrity. Additionally, salinity was found to influence caprock integrity, with higher salinity promoting halite precipitation, which reduces porosity by 0.2 % and has a related effect on permeability, thereby enhancing the sealing efficiency of the caprock and mitigating hydrogen leakage. These quantitative findings provide valuable insights for practical decision-making in UHS projects, highlighting the importance of managing geochemical conditions to enhance caprock stability and minimize leakage risks. Effective optimization of these conditions is essential for ensuring the long-term efficiency and viability of UHS systems.
