محمد كريمي

Hydrogen, as a clean an‎d sustainable energy carrier, plays a pivotal role in the transition to low-carbon energy systems; however, its leakage from subsurface reservoirs through cap rock fractures an‎d aquifers poses a key challenge for safe storage. This study investigates hydrogen leakage behavior through cap rock fracture networks using advanced modeling techniques, including the Embedded Discrete Fracture Model (EDFM), which explicitly incorporates discrete fractures into the computational matrix. The study focused on the effects of static properties (fracture aperture, fracture intensity, an‎d fracture correction factor) an‎d dynamic properties (injection rate, timing, an‎d location). Results showed that among static properties, increasing fracture aperture at constant intensity significantly enhances hydrogen leakage. At constant aperture, increasing fracture intensity also increases leakage, with this effect being less pronounced at smaller apertures an‎d more significant at larger ones. Fracture intensity acts as a controlling factor at larger apertures, leading to leakage similar to that of small apertures with high intensity. Furthermore, increasing the fracture correction factor reduces the leakage rate. For dynamic properties, six injection scenarios were designed. In three scenarios with equal injection durations, increasing the injection rate led to higher leakage. In the other three scenarios with constant injection volume, shorter injection durations resulted in less leakage an‎d proved more cost-effective. A comparison between hydrogen an‎d carbon dioxide leakage showed that hydrogen, due to its lower density an‎d solubility in water, has a higher leakage potential. In modeling, the EDFM method closely matched the performance of the projected EDFM (pEDFM) in high-permeability fractures, but in low-permeability fractures (relative to the matrix), EDFM showed inaccuracies, while pEDFM delivered more accurate results. In field-scale operations, such as drilling two wells on either side of the fracture network, leakage was significantly reduced, though the economic feasibility of drilling additional wells requires eva‎luation. Injection into deeper layers also resulted in lower leakage compared to injections near the cap rock. These findings offer practical solutions for optimizing subsurface hydrogen storage an‎d reducing leakage risks, emphasizing the importance of precise design of static an‎d dynamic parameters.

هيدروژن , شبكه شكاف , آبخوان , سنگ پوش , نشت

hydrogen , fracture network , aquifer , Caprock , Leakage

Karimi

Dr. Fazeli