Offshore Underground Hydrogen Storage: Notional Design and Insights from Subsurface and Surface Facility Perspectives

This paper presents a technical overview and notional design for offshore underground hydrogen storage (UHS) in the Dutch sector of the North Sea. With the anticipated development of offshore wind and hydrogen production at sea via electrolysis, UHS is considered a potential buffer to smooth variability in offshore hydrogen generation and ensure a steady, predictable flow to shore. The concept involves a combined storage system using depleted gas fields (high-capacity, slow response) and salt caverns (low-capacity, fast response). Storage requirements, including working volume, injection and withdrawal rates, and the number of wells are assessed from a subsurface perspective, with particular attention to reservoir transmissivity, well diameter, and maximum erosional velocity. From the surface perspective, estimates are provided for the size and weight of the facilities required for offshore platform installation. Results show that an 8 GW offshore wind farm dedicated to hydrogen production would require 3.1 TWh of working volume in depleted fields and 0.3 TWh in salt caverns. Major challenges include the high number of required wells and the need for extremely large offshore platforms, primarily due to the footprint of the PSA units for gas purification and compressors for tail gas management.