Lithofacies impacts on deformation bands within the Sherwood Sandstone principal aquifer

Deformation bands typically drastically reduce the permeability of sand bodies, impacting gross permeability and ultimate recovery rates for host fluids on human times-scales. This permeability reduction is important in the modelling of flow in the subsurface, and is particularly relevant in the fields of aquifer and reservoir management (hydrocarbons and water), and also in understanding the flow of contaminants through structurally deformed host-rocks. The occurrence of deformation bands is notably associated with high-porosity clastic sandstones, which on a bulk-scale often represent more porous intervals and therefore the better reservoir units in a succession, with typically elevated permeability characteristics. Here we quantitatively evaluate the likelihood of nine individual lithofacies types of aeolian or fluvial origin hosting deformation bands using exposures of the Triassic Sherwood Sandstone Group of northwest England. This study determines that of the nine lithofacies types identified the highly permeable homogeneous clean (silt/clay poor) sandstones formed by (aeolian) grainflow and grainfall processes are most prone to containing deformation bands. Genetically associated and lithologically similar interdunes are identified as the next most prevalent in hosting deformation bands despite an order of magnitude in reduction deformation band frequency. This study highlights the benefits of taking a more detailed lithofacies approach to understanding high permeability aquifers, which could lead to more effective aquifer and reservoir management for areas of the UK with the potential for multiple, conflicting use of the subsurface (e.g., groundwater, CCUS and energy storage).