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.

Geothermal energy is a unique and sustainable renewable resource, distinguished by its substantial reserves, extensive geographical distribution, low-carbon characteristics, and robust stability. The wellbore plays a critical role in geothermal energy production, operating in high-temperature and corrosive environments. However, wellbores often face well integrity (WI) challenges during their lifespans, resulting in financial losses, occupational injuries, and environmental harm. To address these challenges, technological approaches can be utilized to enhance WI, develop preventative and mitigative measures, and improve the overall effectiveness of WI management systems. This literature review explores modern solutions, including advanced inspection technologies, nanotechnology, machine learning (ML), and the Internet of Things (IoT), focusing on their applications to ensure the structural integrity of wells. Advanced inspection technologies, leveraging unmanned vehicles and robotic systems, can optimize accessibility to equipment in unreachable areas, minimize human exposure to hazardous environments, and provide real-time data to assist in detecting equipment cracks and leakages. Nanotechnology such as nano-sensors housed on casings, can remotely observe cement properties, a critical component of WI, effectively enabling early defect detection. Moreover, nanomaterials implemented in wellbore's equipment can strengthen the durability under heavy loads and high temperatures. After the data gathering phase from all available sources, IoT setups, such as the digital twin version of the wellbore, can provide valuable insights into the future phases of the well. By adjusting parameters based on ML predictive results, these setups enable the initiation of effective response plans, enhancing occupational safety and situational awareness.

This study investigates the geothermal potential of the Artu prospect area within the Afar Depression by integrating high-resolution full-tensor gravity gradiometry (FTG) and two-dimensional seismic reflection data. The FTG results highlight distinct gravity anomalies across the Adigala Basin, reflecting subsurface density contrasts associated with volcanic intrusions, complex fault systems and sedimentary layering. Seismic profiles reveal NNW-SSE-trending normal faults that define the structural architecture of the basin and constrain the distribution of magmatic bodies and sedimentary sequences at depths ranging from 1.5 to 4.2 km, with two-way travel times between 1.2 and 3.6 s. These fault systems, characterised by vertical displacements of up to 150 m, intersect with shallow magmatic intrusions, forming zones of enhanced permeability, key conduits for geothermal fluid migration. Thick porous Mesozoic sedimentary formations, interlayered with magmatic sills, emerge as promising geothermal reservoirs. Basin-centred faults (BCFs), aligned with the Goba Magma Chamber (GMC), appear to play a critical role in heat transport and fluid circulation. The findings underscore the value of integrated gravity and seismic data to delineate fault-volcanic intersections and identify viable geothermal targets. This integrated approach provides a solid foundation for future geothermal exploration in rift-related settings such as the Adigala Basin.

Vertical electrical sounding (VES) and magnetic data were analyzed to infer the groundwater system in the Belesa area within the central Main Ethiopian Rift. The analysis is aimed at aiding in determining the groundwater potential for current and future development of groundwater resources within the Belesa area. The analysis of two-dimensional magnetic forward and one-dimensional electrical inverse models aided in locating faults, fractures, and lithological units that may contain groundwater. Lithological logs from nearby boreholes where lithological units had been determined were used to constrain the magnetic and VES models. The VES models and a magnetic derivative (tilt and horizontal) analysis mapped the existence of several possible fractures and faults that may act as either barriers or conduits for groundwater movement. The magnetic and electrical resistivity models indicated a potential aquifer associated with low electrical resistivity values occurring between 120 and 240 m in depth within the weathered and fractured ignimbrites which are bounded by faults, plus an additional potential deeper aquifer within a sandy pumice layer. Low electrical resistivity horizons provide targets for future drilling for water and a base for geophysical surveys that would further delineate the groundwater system in the Belesa area.

Numerous currently operating, past and potential future geothermal energy projects in Australia depend on heat from hot sedimentary aquifer (HSA) sources. The relevant aquifers cover a range of geographical and geological settings. Currently operating geothermal energy projects in Australia (excluding ground source heat pumps) predominantly utilise 40-70 degrees C aquifers in the Gippsland Basin, Otway Basin and Perth Basin. Economic assessments have demonstrated that heat from these sources is significantly cheaper than heat from natural gas. Electrical power has previously been generated using 87-99 degrees C water from aquifers in the Great Artesian Basin in South Australia and Queensland, but those generators are now decommissioned. A project to generate power using >150 degrees C groundwater from deep in the Otway Basin in 2010 was suspended and subsequently abandoned when initial production did not meet commercial requirements. Several new projects, particularly in Western Australia, are in the stage of technical and economic pre-feasibility for geothermal power generation from >150 degrees C groundwater. Preliminary techno-economic assessments may be favourable, but existing regulatory constraints pose major impediments to further development of hot sedimentary aquifers in parts of Australia.

This study aims to provide a comprehensive review of the potential of geothermal energy for producing hydrogen, with a focus on the Australian context where low-temperature geothermal reservoirs, particularly hot sedimentary aquifers (HSAs), are prevalent. The work includes an overview of various geothermal technologies and hydrogen production routes, and evaluates potential alternatives for hydrogen production in terms of energy and exergy efficiency, economic performance, and hydrogen production rate. Values for energy efficiency are reported in the literature to range from 3.51 to 47.04%, 7.4-67.5% for exergy efficiency, a cost ranging from 0.59 to 5.97 USD/kg of hydrogen produced, and a hydrogen production rate ranging from 0.11 to 5857 kg/h. In addition, the article suggests and evaluates multiple metrics to appraise the feasibility of HSAs geothermal reservoirs, with results tailored to Australia but that can be extended to jurisdictions with similar conditions worldwide. Furthermore, the performance of various hydrogen production systems is investigated by considering important operating conditions. Lastly, the key factors and possible solutions associated with the hydrogeological and financial conditions that must be considered in developing hydrogen production using lowtemperature geothermal energy are summarised. This study shows that low-temperature HSAs (similar to 100 degrees C) can still be used for hydrogen generation via supplying power to conventional electrolysis processes by implementing several improvements in heat source temperature and energy conversion efficiency of Organic Rankine Cycle (ORC) power plants. Geothermal production from depleted or even active oilfields can reduce the capital cost of a hydrogen production system by up to 50% due to the use of pre-existing wellbores, under the right operating conditions. Thus, the results of this study bring novel insights in terms of both the opportunities and the challenges in producing clean hydrogen from geothermal energy, applicable not only to the hydro-geological and socio-economic conditions in Australia but also worldwide, exploring the applicability of geothermal energy for clean hydrogen production with similar geothermal potential.

The Gippsland Regional Aquatic Centre (GRAC) opened in the town of Traralgon, Victoria, Australia early in 2021. The GRAC utilizes a geothermal energy heating system as an alternative to conventional natural gas furnaces. We have examined 12 full months of heat production from the geothermal system of the GRAC and compared its economic performance against equivalent heat production by natural gas. The geothermal system—the first of its kind in Victoria—operated at >95% availability over its first year of operation. Our economic assessment indicates that the breakeven price for the geothermal energy is about 35% the equivalent price of natural gas and the payback period for the geothermal system is about five years. The results justify the initial capital outlay by Latrobe City Council and are likely to stimulate further development of geothermal heat systems in the region.

Since 1963, the International Heat Flow Commission has been fostering the compilation of the Global Heat Flow Database to provide reliable heat-flow data. Over time, techniques and methodologies evolved, calling for a reorganization of the database structure and for a reassessment of stored heat-flow data. Here, we provide the results of a collaborative, community-driven approach to set-up a new, quality-approved global heat-flow database. We present background information on how heat-flow is determined and how this important thermal parameter could be systematically evaluated. The latter requires appropriate documentation of metadata to allow the application of a consistent evaluation scheme. The knowledge of basic data (name and coordinates of the site, depth range of temperature measurements, etc.), details on temperature and thermal-conductivity data and possible perturbing effects need to be given. The proposed heat-flow quality evaluation scheme can discriminate between different quality aspects affecting heat flow: numerical uncertainties, methodological uncertainties, and environmental effects. The resulting quality codes allow the evaluation of every stored heat-flow data entry. If mandatory basic data are missing, the entry is marked accordingly. In cases where more than one heat-flow determination is presented for one specific site, and all of them are considered for the site, the poorest evaluation score is inherited to the site level. The required data and the proposed scheme are presented in this paper. Due to the requirements of the newly developed evaluation scheme, the database structure as presented in 2021 has been updated and is available in the appendix of this paper. The new quality scheme will allow a comprehensible evaluation of the stored heat-flow data for the first time.

Periodic revisions of the Global Heat Flow Database (GHFD) take place under the auspices of the International Heat Flow Commission (IHFC) of the International Association of Seismology and Physics of the Earth's Interior (IASPEI). A growing number of heat-flow values, advances in scientific methods, digitization, and improvements in database technologies all warrant a revision of the structure of the GHFD that was last amended in 1976. We present a new structure for the GHFD, which will provide a basis for a reassessment and revision of the existing global heat-flow data set. The database fields within the new structure are described in detail to ensure a common understanding of the respective database entries. The new structure of the database takes advantage of today's possibilities for data management. It supports FAIR and open data principles, including interoperability with external data services, and links to DOI and IGSN numbers and other data resources (e.g., world geological map, world stratigraphic system, and International Ocean Drilling Program data). Aligned with this publication, a restructured version of the existing database is published, which provides a starting point for the upcoming collaborative process of data screening, quality control and revision. In parallel, the IHFC will work on criteria for a new quality scheme that will allow future users of the database to evaluate the quality of the collated heat-flow data based on specific criteria.

The compilation of global heat-flow data is currently under major revision by the International Heat Flow Commission (IHFC) of the International Association of Seismology and Physics of the Earth's Interior (IASPEI). Heat flow represents a fundamental parameter in thermal studies, e.g., the evolution of hydrocarbons or mineral and geothermal resources. Comparable, comprehensible and reliable heat-flow data are of utmost interest also for geophysical and geological studies on the global scale. Here, we present the first results of a stepwise revision of the IHFC Global Heat Flow Database based on a researcher driven, collaborative approach. The first step comprises the review and revision of the most recent database structure established in 1976. The revised structure of the Global Heat Flow Database considers the demands and opportunities presented by the evolution of scientific work, digitization and the breakthroughs in database technologies over the past decades. Based on the new structure, the existing dataset will be re-assessed and new data incorporated. By supporting the ideas of FAIR and open data principles, the new database facilitates interoperability with external data services, like DOI and IGSN numbers, and other data resources (e.g., world geological map, world stratigraphic system, and International Ocean Drilling Program data). We give an overview of the new database and introduce the community workflow of global heat-flow data revision.

It is well established that amplitude decays and phase shifts as a function of depth, frequency, and thermal diffusivity when a periodic surface temperature signal conducts into the ground. In historical practice, this principle has often been employed to estimate soil thermal diffusivity using observations of the dominant diurnal and annual temperature signals. We describe and demonstrate a method to infer thermal diffusivity over a broad bandwidth in the frequency domain using high fidelity time-series ground temperature records. We draw information from thermal signals generated by meteorological events over weeks and months, as well as the dominant diurnal signal. Both the decay in amplitude and shift in phase of each frequency band contribute points to plots that define linear functions relative to a parameter that incorporates frequency and depth. Linear regression through the points gives the magnitude and uncertainty of the slope of the function, where the slope is equal to the inverse square root of the average thermal diffusivity over the sampled time-period and depth interval. This allows statistical quantification of the uncertainty in the thermal diffusivity estimate. Furthermore, our method delineates depth intervals where nonconductive processes significantly affect heat transfer. Examples are presented for a dry desert soil in South Australia and the floor of a tropical alpine forest in Mexico.

The mean land-surface temperature represents an important boundary condition for many geothermal studies. This boundary is particularly important to help constrain the models made to analyse resource systems, many of which are shallow in nature and observe relatively small thermal gradients. Consequently, a mean land-surface temperature map of the Australian continent has been produced from 13 years of MODIS satellite imagery, for the period 2003-2015. The map shows good agreement with independent methods of estimating mean land surface temperature, including borehole surface -temperature extrapolation and long-term, near-surface ground measurements. In comparison to previously used methods of estimating mean land-surface temperature, our new estimates are up to 12 degrees C warmer. The MODIS-based method presented in this study provides spatially continuous estimates of land-surface temperature that can be incorporated as the surface thermal boundary condition in geothermal studies. The method is also able to provide a quantification of the uncertainties expected in the application of these estimates for the purposes of thermal modelling.