Mapping thermal conductivity in Ireland to determine geothermal potential

High-quality maps of the geothermal gradient and temperature are essential when assessing the geothermal potential of a region. However, determining geothermal potential is a challenge when direct measurements of in situ temperature and thermal property information are sparse, as is the case in Ireland. In addition, individual geophysical methods are sensitive to a range of parameters, not solely temperature. We develop a novel approach to determine the geothermal gradient using a joint geophysical-petrological thermochemical inversion (Chambers et al. Tectonophysics (2023) & Fullea et al. GJI (2021)), which requires seismic surface wave data, thermal property data, and additional geophysical and petrophysical datasets. The multi-parameter models produced by the integrated inversions fit the surface-wave, heat flow and additional data, revealing the temperature, lithospheric structure and geothermal gradient within the crust and mantle.

Here we present the new methodology and resulting models of Ireland’s subsurface temperature with a focus on new thermal conductivity measurements and their impact on temperature. A new map of thermal conductivity (TC) for all of Ireland was generated using all existing measurements of thermal conductivity, in addition to 609 new measurements from the optical scanning technique and 86 using the Divided Bar Apparatus (DB) which we use in the inversion. Our new methodology produces results comparable to past temperature and geophysical measurements and models. Importantly, the maps are within error of direct borehole temperature measurements, providing confidence in the results. Lithospheric and crustal thickness play a key control on the temperature gradient with areas of thinner lithosphere resulting in elevated geotherms. In some locations, we observe geotherms elevated beyond expectations which result from high radiogenic heat production from granitic and muddy limestone rocks. This new methodology provides a robust workflow for determining the geothermal potential in areas with limited direct measurements. The final temperature model updates previous maps of Ireland and will be used for future geothermal exploration and utilisation.