Assessing underground hydrogen storage with natural gas using numerical simulations

• Applicant: Professor Dr.-Ing. Anozie Ebigbo
• Subject Area: Hydrogeology, Hydrology, Limnology, Urban Water Management, Water Chemistry, Integrated Water Resources Management ; Geotechnics, Hydraulic Engineering
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 568130664

The intermittent nature of some renewable energy sources means that the imminent transition to renewables will require large-scale energy storage. Hydrogen can serve as the fuel of the future. However, large-scale storage of hydrogen is not trivial. The potential storage capacity in the subsurface -- e.g. in depleted oil and gas reservoirs, deep saline aquifers -- is very large and can be used for underground hydrogen storage. While one can transfer know-how and technology from natural gas storage and underground carbon storage, some of the challenges underground hydrogen storage faces are different. Compared to subsurface water, hydrogen has a very low density and viscosity. Consequently, a hydrogen plume will experience strong buoyancy forces (i.e. high leakage potential). Hydrogen injection into the a heterogeneous reservoir can lead to a spreading/dispersal of the hydrogen plume, making it more difficult to recover the hydrogen during the production phase. In addition, water upconing towards the extraction borehole can occur. This could lead to the influx of water into the borehole. Further, some stored hydrogen will remain underground, trapped by capillary forces. The cyclic injection/extraction process leads to a constant alternation between drainage (gas displaces water) and imbibition (water displaces gas), potentially increasing the trapping of hydrogen. It has been suggested that existing natural gas pipe networks could be used for the transport of hydrogen. The gases would be transported as a mixture and separated afterwards. The storage of hydrogen/methane gas mixtures may be advantageous since the mixture would have a higher density and viscosity than pure hydrogen. One way to minimise the amount of water extracted during hydrogen production is the use of a cushion gas, usually a cheaper and denser gas like nitrogen or more methane. This concept is well known in underground gas storage. In this project, I propose the use of realistic numerical modelling of the two-phase flow processes in a sandstone reservoir to elucidate potential advantages of the mixed hydrogen/methane storage may have over pure hydrogen storage. Specific questions that arise in this regard are: 1) How does the composition of the hydrogen/methane mixture affect the storage efficiency? 2) How much more effective can a cushion gas be in minimising the capillary trapping of the stored gas and the unwanted extraction of water in the mixed gas storage as compared to pure hydrogen storage? 3) How strong is the effect of large-scale geological heterogeneities which form baffles and/or preferential flow paths on the storage efficiency?

• DFG Programme: Research Grants
• International Connection: China, Switzerland
• Cooperation Partners: Dr. Mahmoud Hefny; Professor Dr. Chaozhong Qin