Unlocking Low-Carbon Heat: Geothermal Feasibility and Thermal Breakthrough in Carboniferous Sandstone Aquifers

Decarbonisation is crucial for mitigating climate change, with ground source heat pumps (GSHPs) playing a key role in reducing reliance on gas for space heating. This study investigates the potential of an open-loop GSHP system in the Carboniferous Millstone Grit of Ilkley, West Yorkshire, using Ilkley Lido and surrounding sports facilities as an example heating demand. The feasibility of systems installed at depths less than 150 m is examined, considering both shallow and deeper geological conditions. Available data on subsurface geology, hydrogeology, and geothermal gradients are utilised to characterise the formations and target depths, with cross-sectional models developed to assess the potential. The Marchup Grit aquifer is identified as the primary target due to its relatively shallow depth (~90 m), expected subsurface temperature (~14.5 °C), and moderate transmissivity. Additional geothermal potential is also considered in the Warley Wise Grit and Pendleside Limestone. The study contrasts borehole and field data with literature findings, including measurements at outcrop level of the Marchup Grit. To assess the feasibility of an open-loop GSHP system, a doublet configuration is simulated, matching the estimated heat demand of the facilities. The results demonstrate that an open-loop doublet system is conditionally feasible within the Marchup Grit aquifer; however, long-term operational performance remains sensitive to thermal feedback (estimated at ~22 years analytically for a 300 m well spacing and 8–10 years numerically under a 130 m minimum spacing constraint at peak abstraction rates). By reducing abstraction to 70% of the peak heating demand, long-term sustainability can be improved. Overall, while the system exhibits preliminary potential, commercial implementation remains subject to confirmatory site-specific borehole drilling, hydrochemical sampling, and long-duration pumping tests to validate reservoir capacity and optimise system longevity.