Ghaedi Mojtaba, Gholami Raoof
Department of Energy Resources, University of Stavanger, Stavanger, Norway.
Sci Rep. 2025 Jan 2;15(1):185. doi: 10.1038/s41598-024-84505-x.
Salt caverns are widely regarded as a suitable option for the underground storage of hydrogen. However, an accurate assessment of the hydrogen leakage through the walls of salt caverns into the surrounding formations remains crucial. In this work, the flow of hydrogen into the surrounding formation is evaluated by assuming that salt rock consists of bundles of tortuous nano-capillary tubes. A formulation was then proposed to model the flow in linear and radial domains. The formulations are based on a newly proposed unified gas flow model that is valid for the entire range of Knudsen numbers and accounts for gas slippage, bulk diffusion, and Knudsen diffusion. A finite-difference approximation with an iterative procedure was then used to treat the nonlinearity and solve the presented formulations. The formulations were validated against the experimental data reported in the literature. The results obtained indicated that for hydrogen flow over a wide range of pore radii and operating pressures and temperatures, the slippage flow regime must be considered. In a salt cavern with relevant dimensions and operating conditions, the cumulative hydrogen leakage after 30 years of cyclic storage was only 0.36% of the maximum storage capacity. It was also noticed that most of the leaked hydrogen would flow back into the salt cavern at times when the pressure in the salt cavern is lower than the surrounding pressure, e.g. during production and subsequent idle times. At low storage pressure and very tight salt rock, diffusion was the most important mechanism for hydrogen transport. At a high pressure though, viscous flow became the predominant leakage mechanism. The presence of a thin interlayer such as mudstone, carbonate, and anhydrite in the body of the salt rock can have a significant impact on the amount of leakage. It appeared that although increasing the maximum operating pressure from 120 to 135 bar only led to an 11.9% increase in the maximum storage capacity, the hydrogen loss increased significantly from 0.007% at 120 bar to 0.36% at 135 bar. Furthermore, although the absolute leakage rate for natural gas storage was higher than that for hydrogen storage, the relative leakage rate in relation to the maximum salt cavern capacity was much lower. The leakage range was also lower for natural gas storage compared to hydrogen storage. The formulations presented and the results obtained in this study can help to have a better understanding of the salt caverns when it comes to large-scale hydrogen storage.
盐穴被广泛认为是地下储存氢气的合适选择。然而，准确评估氢气通过盐穴壁面泄漏到周围地层的情况仍然至关重要。在这项工作中，通过假设盐岩由曲折的纳米毛细管束组成来评估氢气向周围地层的流动。然后提出了一个公式来模拟线性和径向区域的流动。这些公式基于一个新提出的统一气体流动模型，该模型对整个克努森数范围有效，并考虑了气体滑移、体扩散和克努森扩散。然后使用带有迭代过程的有限差分近似来处理非线性并求解所提出的公式。这些公式根据文献中报道的实验数据进行了验证。获得的结果表明，对于在广泛的孔隙半径、操作压力和温度范围内的氢气流动，必须考虑滑移流态。在具有相关尺寸和操作条件的盐穴中，循环储存30年后的氢气累积泄漏量仅为最大储存容量的0.36%。还注意到，在盐穴压力低于周围压力时，例如在生产和随后的闲置时间，大部分泄漏的氢气会回流到盐穴中。在低储存压力和非常致密的盐岩条件下，扩散是氢气传输的最重要机制。然而，在高压下，粘性流成为主要的泄漏机制。盐岩体中存在诸如泥岩、碳酸盐和硬石膏等薄夹层会对泄漏量产生重大影响。似乎虽然将最大操作压力从120巴提高到135巴仅导致最大储存容量增加11.9%，但氢气损失却从120巴时的0.007%显著增加到135巴时的0.36%。此外，虽然天然气储存的绝对泄漏率高于氢气储存，但相对于盐穴最大容量的相对泄漏率要低得多。与氢气储存相比，天然气储存的泄漏范围也更低。本研究中提出的公式和获得的结果有助于在大规模氢气储存方面更好地理解盐穴。
