Thermal structure and geothermal potential of the onshore Gippsland basin inferred from 3D conductive heat flow modelling

Understanding spatial and depth-dependent variations in thermal conductivity is essential for accurate geothermal modelling in sedimentary basins. This study investigates the thermal structure and geothermal potential of the onshore Gippsland Basin, southeastern Australia, by integrating published thermal-property datasets with 3D steady-state conductive modelling using the open-source Underworld3 framework. Lithology-dependent mean thermal conductivity values for the Latrobe Valley Subgroup were derived from borehole lithological proportions and ranged from 0.56 to 1.21 W/m·K, reflecting strong lateral heterogeneity associated with variable coal content. The thermal model incorporates spatially variable land surface temperature (LST), interval temperature logs, bottom-hole temperature data, and laterally varying basal temperatures extrapolated using one-dimensional conductive heat flow models and interpolated across the basin. Model results predict surface temperatures ranging from approximately 11.54 to 20.68°C and laterally variable basal temperatures of approximately 120 to 256°C at 5,000 m depth, reflecting the combined influence of thermal conductivity, heat flow, and surface temperature variability. Temperatures at the top of the Cenozoic-aged geothermal source rock range from approximately 14 to 65°C, indicating favourable conditions for low-enthalpy geothermal applications. Model constraining against borehole temperature data demonstrates good agreement between measured and modelled thermal profiles. Volumetric heat-in-place calculations indicate that the Cenozoic-aged geothermal source contains maximum values of approximately 31 exajoules (EJ) of stored thermal energy. These results highlight the importance of incorporating spatially variable thermal conductivity and non-uniform basal boundary conditions into geothermal models and provide a refined framework for geothermal assessment in the onshore Gippsland Basin and other coal-bearing sedimentary basins.