The Sherwood Sandstone Group as a potential geothermal aquifer across Northern Ireland

The Triassic Sherwood Sandstone Group (SSG) is a thick unit of sandstones with mostly good reservoir quality. Deposition in fluvial and aeolian environments is reflected in a range of sedimentary facies that have impacted the resulting reservoir quality, which has been further reduced or enhanced by burial-related processes. Data from water, hydrocarbon and geothermal exploration boreholes across Northern Ireland have helped to increase our understanding of SSG aquifers as potential future geothermal energy resources. The SSG is up to 650 m thick and is widely distributed across the Permo-Triassic basins in NE Northern Ireland. The basins are mostly concealed beneath Palaeogene basalts that degrade seismic data quality, so that potential field geophysics, structural and borehole data have been used to model SSG depths. Thin section and core analysis have been carried out to assess the spatial distribution of the best reservoir quality. For many years the SSG was an important source of water for the industrial growth of Belfast and subsequently the sandstones formed the principal target for limited hydrocarbon exploration. The sandstone aquifer is already used for heating and cooling, using heat pump technology, in the Greater Belfast area, where it is relatively shallow and there is potential for this type of geothermal energy use to grow. However, information acquired since the 1980s also indicates hot aquifers at depth within the SSG may represent a far greater resource that could be used as a sustainable low carbon energy source for direct heating applications via the deployment of heat networks.