Hydrogen usage and storage may contribute to reducing greenhouse gas emissions by decarbonising heating and transport and by offering significant energy storage to balance variable renewable energy supply. Underground storage of hydrogen is established in underground salt caverns, but these have restricted geographical locations within the UK and cannot deliver the required capacity. Hydrogen storage in porous geological formations has significant potential to deliver both the capacity and local positioning. This study investigates the potential for storage of hydrogen in porous subsurface media in Scotland. We introduce for the first time the concept of the hydrogen storage play. A geological combination including reservoir, seal and trap that provides the optimum hydrogen storage reservoir conditions that will be potential targets for future pilot, and commercial, hydrogen storage projects. We investigate three conceptual hydrogen storage plays in the Midland Valley of Scotland, an area chosen primarily because it contains the most extensive onshore sedimentary deposits in Scotland, with the added benefit of being close to potential consumers in the cities of Glasgow and Edinburgh. The formations assessed are of Devonian and Carboniferous age. The Devonian storage play offers vast storage capacity but its validity is uncertain due to due to a lack of geological data. The two Carboniferous plays have less capacity but the abundant data produced by the hydrocarbon industry makes our suitability assessment of these plays relatively certain. We conclude that the Carboniferous age sedimentary deposits of the D'Arcy-Cousland Anticline and the Balgonie Anticline close to Edinburgh will make suitable hydrogen storage sites and are ideal for an early hydrogen storage research project.

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Discovery of the Breagh gas field in the Southern North Sea (SNS) has demonstrated the potential that the Lower Carboniferous (Visean, 346.7–330.9 Ma) Farne Group reservoirs have to contribute to the UK's future energy mix. New biostratigraphic correlations provide a basis to compare Asbian and Brigantian sedimentary cores from the Breagh Field and age-equivalent sediments exposed on the Northumberland Coast, which has proved critical in gaining an understanding of exploration and development opportunities. Thirteen facies associations characterize the mixed carbonate–siliciclastic system, grouped into: marine, delta front, delta shoreface, lower delta plain and upper delta plain gross depositional environments. The facies associations are interpreted as depositing in a mixed carbonate and siliciclastic fluvio-deltaic environment, and are arranged into coarsening- and cleaning-upward cycles (parasequences) bounded by flooding surfaces. Most cycles are characterized by mouth bars, distributary channels, interdistributary bays and common braided rivers, interpreted as river-dominated deltaic deposits. Some cycles include rare shoreface and tidally-influenced deposits, interpreted as river-dominated and wave- or tide-influenced deltaic deposits. The depositional processes that formed each cycle have important implications for the reservoir net/gross ratio (where this ratio indicates the proportion of sandstone beds in a cycle), thickness and lateral extent. The deltaic deposits were controlled by a combination of tectonic and eustatic (allocyclic) events and delta avulsion (autocyclic) processes, and are likely to reflect a changing tectonic regime, from extension within elongate fault-bounded basins (synrift) to passive regional thermal subsidence (post-rift). Deep incision by the Base Permian Unconformity across the Breagh Field has removed the Westphalian, Namurian and upper Visean, to leave the more prospective thicker clastic reservoirs within closure. Thematic collection: This article is part of the Under-explored plays and frontier basins of the UK continental shelf collection available at: https://www.lyellcollection.org/cc/under-explored-plays-and-frontier-basins-of-the-uk-continental-shelf

The Darende Basin is an excellent example of an important, but little known, type of sedimentary basin that can form on the top of emplaced ophiolites prior to and during continental collision. The basin formation was preceded by southward emplacement of accretionary mélange and ophiolites onto the Tauride carbonate platform during latest Cretaceous. Sedimentation began during the Maastrichtian with non-marine clastic sediments accumulating in palaeovalleys. This was followed by a Maastrichtian marine transgression, triggered by extension along the basin margins. Rudist-rich patch reefs and a carbonate shelf developed in different areas. A second transgression during the Mid-Eocene was preceded by emergence, a hiatus (Paleocene), localized faulting and low-angle (<5–10°) tilting. Middle Eocene hemipelagic marls, shallow-marine Nummulites-rich carbonates, calciturbidites and sparse alkaline volcanism culminated in Late Eocene shallowing, emergence and then deformation. The first phase of basin development (Maastrichtian) is seen as extensional, related to slab-pull that resulted from northward subduction of remnant oceanic lithosphere beneath Eurasia in the Pontides to the north. The second phase of basin development (Mid–Late Eocene) is explained by crustal downflexure to form an under-filled foreland basin during the final collision of the Tauride continent with Eurasia. Basin uplift was delayed until after a Mid-Miocene marine incursion.Supplementary material:Full results of the palaeontological determination of collected samples from the Eocene aged sedimentary rocks of the Darende Basin are available at www.geolsoc.org.uk/SUP18544

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