Late Permian Evaporite Facies Variation in the Forth Approaches Basin, North Sea: Implications for Hydrogen Storage

Hydrogen is expected to play a key role in decarbonising industry and storing energy from intermittent sources such as wind energy. Underground salt caverns are an attractive target for storage due to large volumes and effective sealing capacity. Despite ambitious goals to become a world-leader in hydrogen, there are no onshore salt basins in Scotland. Therefore, the offshore Forth Approaches Basin (FAB), currently undergoing development of the Seagreen wind farm, could provide a critical storage site. Re-evaluation of petrophysical data from five legacy hydrocarbon wells allowed an updated assessment of the composition and variability of the Late Permian Zechstein evaporite sequence. Well analysis is combined with seismic interpretation to understand the salt bodies and their suitability for solution mining. Three halite formations are identified: (1) The Stassfurt Halite which has insufficient thickness for solution mining; (2) The Leine Halite that comprises three sub-units with a KCl-dominated unit separating two halite-dominated units; (3) The Aller Halite only identified in the centre of the FAB. Where halokinesis has occurred, the Leine Halite reaches sufficient thicknesses (>300m) and purity for salt cavern placement, however heterogeneities are challenging to predict. Layered evaporites only reach sufficient thickness where the Aller Halite is present and could be developed with the underlying Leine Halite. Heterogeneities can be correlated across wells within the layered sequences aiding prediction. A strong understanding of evaporite facies distribution is required to ensure halite bodies are suitable for safe and economic solution mining in the FAB and other salt basins globally. Thematic collection: This article is part of the Hydrogen as a future energy source collection available at: https://www.lyellcollection.org/topic/collections/hydrogen