Numerical Model for Underground Hydrogen Storage in Cased Boreholes

The decrease in generation costs of renewable energy, combined with advances in electrolyser technologies, suggest that green hydrogen production may be a viable option in the ongoing energy transition. Yet, a green hydrogen economy requires not only production solutions but also storage options, which prove to be challenging. An underexplored solution is the underground storage of hydrogen gas (H-2) in cased boreholes or shafts. Its integration would bring versatility in the implementation, and large applicability since it does not require a particular geological context. The objective of this paper is to evaluate the technical viability of this new storage technology. Accurate prediction of temperature and pressure variations is essential for design, materials selection and safety reasons. This work uses numerical models based on the mass and energy conservation equations to simulate hydrogen storage operations in cased boreholes. The study shows that the heat transfer at the cavity walls strongly affects temperature and pressure variations. This effect is accentuated by a borehole's geometry providing significant contact area. Thus, such technology mitigates extreme pressure and temperature variations and yields a higher hydrogen density than conventional caverns for a given pressure constraint. Results show that with a radius of 0.2 m, a hydrogen density of 30 kgm(-3) can be attained at amaximum pressure of 50 MPa. The response of the system in terms of maximum temperature and pressure is relatively linear with an injection over 4 h but quickly becomes non-linear with a shorter injection time. The optimization of the initial storage conditions appears essential to minimize the cooling cost and maximize the storage mass.