Deformation bands can affect the permeability within reservoir sand bodies, resulting in reductions in hydrocarbon flow and impacting recovery rates. This permeability reduction also impacts water extraction and limits contaminant dispersal. The occurrence of deformation bands is notably associated with high-porosity, clastic sandstones, which on a bulk scale often represent the better reservoir units in a succession, with elevated porosity and permeability characteristics. This study quantitatively evaluates the likelihood of nine individual lithofacies types of aeolian or fluvial origin hosting deformation bands using exposures of the Triassic, Sherwood Sandstone Group of northwestern England (United Kingdom). Specifically, this study determines that of the nine lithofacies types identified, the homogeneous, clean (silt/clay poor) sandstones formed by (aeolian) grain -flow and grain-fall processes are most prone to containing deformation bands. The genetically associated and lithologically similar interdunes are identified as the next most prevalent for hosting deformation bands despite an order of magnitude reduction in deformation band frequency when normalized to volumes of lithofacies present, relative to the aforementioned grain -flow and grain-fall lithofacies. Of the nine lithofacies types observed, all, with exception of aeolian grain -flow and grain-fall facies, were considered underrepresented relative to the total number of deformation bands observed at outcrop, with grain-fall and grain -flow facies at every locality hosting at least 85% of the deformation bands present.

Hydrogen can be used to enable decarbonisation of challenging applications such as provision of heat, and as a fuel for heavy transport. The UK has set out a strategy for developing a new low carbon hydrogen sector by 2030. Underground storage will be a key component of any regional or national hydrogen network because of the variability of both supply and demand across different end-use applications. For storage of pure hydrogen, salt caverns currently remain the only commercially proven subsurface storage technology implemented at scale. A new network of hydrogen storage caverns will therefore be required to service a low carbon hydrogen network. To facilitate planning for such systems, this study presents a modelling approach used to evaluate the UK's theoretical hydrogen storage capacity in new salt caverns in bedded rock salt. The findings suggest an upper bound potential for hydrogen storage exceeding 64 million tonnes, providing 2150 TWh of storage capacity, distributed in three discrete salt basins in the UK. The modelled cavern capacity has been interrogated to identify the practical inter-seasonal storage capacity suitable for integration in a hydrogen transmission system. Depending on cavern spacing, a peak load deliverability of between 957 and 1876 GW is technically possible with over 70% of the potential found in the East Yorkshire and Humber region. The range of geologic uncertainty affecting the estimates is approximately +/- 36%. In principle, the peak domestic heating demand of approximately 170 GW across the UK can be met using the hydrogen withdrawn from caverns alone, albeit in practice the storage potential is unevenly distributed. The analysis indicates that the availability of salt cavern storage potential does not present a limiting constraint for the development of a low-carbon hydrogen network in the UK. The general framework presented in this paper can be applied to other regions to estimate region-specific hydrogen storage potential in salt caverns.

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The increasing integration of large-scale electricity generation from renewable energy sources in the grid requires support through cheap, reliable, and accessible bulk energy storage technologies, delivering large amounts of electricity both quickly and over extended periods. Compressed air energy storage (CAES) represents such a storage option, with three commercial facilities using salt caverns for storage operational in Germany, the US, and Canada, with CAES now being actively considered in many countries. Massively bedded halite deposits exist in the UK and already host, or are considered for, solution-mined underground gas storage (UGS) caverns. We have assessed those with proven UGS potential for CAES purposes, using a tool developed during the EPSRC-funded IMAGES project, equations for which were validated using operational data from the Huntorf CAES plant. From a calculated total theoretical ‘static’ (one-fill) storage capacity exceeding that of UK electricity demand of ≈300 TWh in 2018, filtering of results suggests a minimum of several tens of TWh exergy storage in salt caverns, which when co-located with renewable energy sources, or connected to the grid for off-peak electricity, offers significant storage contributions to support the UK electricity grid and decarbonisation efforts.

Abstract. Borehole core provides detailed vertical data which is used to interpret subsurface sand body architectures, but assumptions are made on the relationship between the lateral and vertical thickness, and the interconnectivity of units. The sedimentological complexity of the Sherwood Sandstone Group succession in this area, passing between aeolian and fluvial packages creates local- to regional-scale heterogeneities which will impact flow pathways within the rockmass. Measured thickness in boreholes might represent an architectural element's true maximum thickness or more likely, a partial thickness as a result of incision by overlying facies types or as a result of the borehole sitting towards the margins of individual elements (e.g. tapering margin of channel elements). Length and thickness data were measured from a suite of primary core data and secondary published outcrop studies in north-west England. The addition of outcrop studies in combination with the borehole data provides a dataset from which the likely lateral extent of the architectural frameworks within the Triassic sandstones can be extrapolated. The interpreted high resolution sub-seismic architecture contributes to an increased understanding of flow pathways and the effect these may have on groundwater as well as sustainable energy technologies such as low-temperature geothermal aquifers, carbon storage and energy storage.

The physical properties of the Mercia Mudstone Group (MMG) are of interest to Carbon Capture and Storage (CCS) in the UK, both in terms of the sealing capacity of certain horizons and in order to assess scenarios involving CO2 migration in the overburden above potential CCS sites. In this study, the hydromechanical properties of MMG samples from the Larne Basin, Northern Ireland, were directly measured under steady-state conditions. Test samples were found to be good seals, with hydraulic permeabilities ranging from ≈2.1 x 10−18 to 8.4 x 10−21 m2 (2.1 x 10−3 to 8.5 x 10−6 mD). A detailed examination of the consolidation behaviour of the material yielded values for compressibility, hydraulic permeability and specific storage, as a function of effective pressure. Consolidation testing also provided preconsolidation pressure values of between 30 and 37 MPa. Test data were fitted to a linear elastic model using a two-dimension finite element approach, yielding hydraulic permeability and Young's Modulus, as a function of effective pressure. Findings suggest localisation of flow, due to small-scale heterogeneity, may play a role even in relatively large test samples. Results also highlight the impact of methodology on resulting permeabilities and the importance of using values measured at boundary conditions appropriate for the specific application. Critical state envelopes were derived from test data and used to conduct a scenario analysis, considering a range of stress paths, to examine the impacts of depletion and reinflation during CO2 injection. Initial stress conditions, stress path gradient and caprock heterogeneity were all found to be influencing factors on the potential for yield during depletion and the resulting deformation mode. The response to CO2 injection is less clear, but will be impacted by the initial caprock permeability and resulting drainage response. An awareness of these controls on caprock performance during stress path changes may aid in the selection of depleted CCS sites with geomechanically favourable characteristics for reinjection.

This paper describes a laboratory study of the hydro-mechanical properties of samples from the Sherwood Sandstone Group (SSG), an onshore analogue of the finer grained, lower porosity portions that make up the Bunter Sandstone Formation (BSF). The study provides a yield envelope for this sandstone, and demonstrates that it is a competent sandstone at relevant reservoir depths. A theoretical yield envelope has been calculated based on the anticipated in situ stress induced by depletion and reinjection, showing that only the high porosity (35%), large grain diameter (290µm) end-member of the BSF is likely to result in deformation of the reservoir rock. Stress analysis of four fields within the Southern North Sea suggest that depletion of 10MPa will not result in permanent deformation of the reservoirs assuming similar porosity and grainsize characteristics to the SSG tested. Furthermore, re-inflation is unlikely to result in permanent deformation should the injection pressure not exceed the initial pre-production reservoir pore pressure.

•An estimating exergy storage method of cavern-based CAES is developed.•Two cavern operational scenarios, isochoric and isobaric cavern, are studied.•Air temperature variations in cavern significantly affect the exergy storage.•Uncompensated isobaric cavern has high exergy storage per unit cavern volume.•A case study of Hornsea gas storage indicated the potential of CAES in the UK.

There is an increasing need for underground storage of natural gas (and potentially hydrogen) to meet the UK’s energy demands and ensure its energy security. In addition, the growth of renewable energy technologies, such as wind power, will be facilitated by the development of grid-scale energy storage facilities to balance grid demand. One solution lies in creating large-scale compressed-air energy storage (CAES) facilities underground. Whilst a number of lithologies offer storage potential, only three operational CAES facilities exist in the UK. They are constructed in specifically designed solution-mined salt (halite) caverns, similar to those currently used for natural gas storage. The influences exerted on salt dissolution by petrology, structure and fabric during cavern construction are not fully understood, with some occurences of caverns with noncircular cross-sections being less than optimum for gas storage and especially CAES.