The Australian Geothermal Association compiled data on the installed capacity of direct-use geothermal and geoexchange systems in Australia, including large-scale ground source heat pumps and hot sedimentary applications through to December 2018. Large-scale direct-use hot sedimentary aquifer systems includes systems to heat swimming pools or provide hydronic heating systems. In geoexchange systems, the Earth acts as a heat source or a heat sink, exploiting the temperature difference between the surface (atmosphere) and at depth. The temperature of the Earth just a few metres below the surface is much more consistent than atmospheric temperature, especially in seasonal climates. These resources do not require the addition of geothermal heat.

The Australian Geothermal Association compiled data on the installed capacity of direct-use geothermal and geoexchange systems in Australia, including large-scale ground source heat pumps and hot sedimentary applications through to December 2018. Large-scale direct-use hot sedimentary aquifer systems includes systems to heat swimming pools or provide hydronic heating systems. In geoexchange systems, the Earth acts as a heat source or a heat sink, exploiting the temperature difference between the surface (atmosphere) and at depth. The temperature of the Earth just a few metres below the surface is much more consistent than atmospheric temperature, especially in seasonal climates. These resources do not require the addition of geothermal heat.

Geothermal energy is a renewable energy technology reported to have a large potential resource base. However, existing geothermal data for Australia (borehole temperatures and heat flow determinations), are limited and collection of additional data is both time consuming and restricted to accessing to wells drilled for other purposes. It is therefore important to develop "deposit" or resource models to aid exploration; improving the quality of subsurface thermal estimates, and helping to identify the distal footprints of geothermal systems. Conceptually, the fundamental requirements of a geothermal system are well understood. However, the complex interplay between the various elements makes it difficult to compare different geographical regions and to assess their relative prospectively. As such, the results of some 130,000 synthetic thermal-modelling runs have been used to calibrate a new tool called the 'Geothermal Calculator'. The Calculator acts as an emulator, or surrogate model, falling into a class of functions which seek to approximate the input / output behaviour of more-complex systems. This presentation will explore the mechanics of the Calculator, before examining some of its possible uses; from simple point-spot estimates to the broader continental scale. The functionality of the Geothermal Calculator presents a significant step forward in our ability to produce subsurface temperature estimates, and represents a notable milestone in the pathway to realising our subsurface geothermal energy potential.

A new approach for developing a 3D temperature map of the Australian continent is currently being developed that relies on combining available proxy data using high-performance computing and large continental-scale datasets. The new modelling approach brings together the current national-scale knowledge of datasets collected by Geoscience Australia and others, including AusMoho, OZTemp, OzSeebase, OZCHEM, surface temperature, the Surface Geology of Australia, sedimentary basins' thermal conductivity and the National Gravity Map of Australia. Bringing together such a range of datasets provides a geoscientific basis by which to estimate temperature in regions where direct observations are not available. Furthermore, the performance of computing facilities, such as the National Computational Infrastructure, is enabling insights into the nature of Australia's geothermal resources which had not been previously available. This should include developing an understanding of the errors involved in such a study through the quantification of uncertainties. Currently the new approach is being run as a pilot study however, initial results are encouraging. The pilot study has been able to reproduce the temperature trends observed in areas that have been heavily constrained by bore-hole observations. Furthermore, a number of areas have now been identified, due to the difference in their estimated temperature from previous methods, which warrant further study.

The Virtual Geophysics Laboratory (VGL) is an environment that was developed as a data discovery and delivery facility with software and computing facilities. This design enables geoscientists to store, discover, retrieve and process datasets. Recent developments are expanding the VGL to incorporate the functionality of the Underworld software. Underworld is open source, parallel software capable of calculating the 3D temperature distribution in the crust. Numerical modelling of temperature is a tool that can be used to predict the temperature distribution at depth between and beneath measurement points based on a 3D geological map. Computing models on a regional scale tends to be computationally intensive, and high-performance computing (HPC) facilities are often required to run computations at full resolution. In order to assess uncertainty quantitatively, HPC facilities are almost always a requirement. The new developments to VGL will facilitate the discovery and access to 3D geological maps. It will also provide easier access to the Underworld software, and will provide the high performance and cloud computing facilities (hosted at the National Computing Infrastructure and elsewhere) required to run large models. The metadata associated with each run performed using VGL is automatically stored, and therefore runs completed on VGL will be repeatable and testable.

To be technically viable, a geothermal energy prospect has two requirements: sufficiently high temperatures at economically-accessible depths; and a viable reservoir from which to extract the heat by flowing fluid at a suitable rate. In recent years, Geoscience Australia (GA) has applied conductive thermal modelling to 3D geological maps to improve predictive targeting of elevated temperatures in the Australian crust. GA is developing capability to improve targeting of favourable reservoir characteristics, using a combination of geothermal modelling techniques, and the use of geophysical and other geoscience data. GA's assessments of crustal temperature potential have incorporated temperature measurements, heat flow data, thermal conductivity measurements and heat production estimates based on geochemistry data. They have also incorporated other datasets such as outcrop geology, drillhole intersections, seismic and gravity data. GA's initial assessment of North Queensland was qualitative and based on a 2D GIS approach. Subsequent assessments were quantitative and based on 3D thermal models, however, due to computational restrictions; uncertainty in the temperature predictions was assessed only qualitatively. More recently, thermal modelling was conducted on a 3D geological map of the Cooper Basin region in South Australia and Queensland (Meixner et al., 2012) using the SHEMAT software (Clauser, 2003). Uncertainty in the temperature predictions was estimated via a Monte-Carlo based approach using the National Computational Infrastructure (NCI) at the Australian National University. The second requirement for a viable geothermal energy prospect is reservoir potential. GA is developing capability to identify reservoir potential using two related approaches. The first involves use of the TOUGH2-MP reservoir modelling code on the NCI. This code will be used to simulate fluid-flow in synthetic geothermal reservoirs with varying geometries and permeability structures, to identify the most desirable characteristics. The second approach involves application of geophysical methods to improve predictive targeting of geothermal reservoirs. GA has used numerical modelling techniques to improve predictive targeting of elevated crustal temperatures and is now building capability to assist predictive targeting of favourable reservoir characteristics. This will allow new geothermal targets to be identified based on the two geological requirements for a successful geothermal prospect. By applying this approach on a national scale, GA will be able to provide an integrated, Australia-wide assessment of geothermal potential. Clauser, C. (ed.), 2003. Numerical Simulation of Reactive Flow in Hot Aquifers: SHEMAT and Processing SHEMAT. Springer-Verlag: Berlin Heidelberg. Meixner, A.J., Kirkby, A.L., Lescinsky, D.T., and Horspool, N., 2012b. The Cooper Basin 3D Map Version 2: Thermal modelling and temperature uncertainty. Record 2012/60. Geoscience Australia: Canberra.

A new approach for developing a 3D temperature map of the Australian continent has been trialled that combines available proxy data using high-performance computing and large continental-scale datasets. The Thermal Map from Assessed Proxies (TherMAP) is a new 3D modelling approach that brings together up-to-date national-scale datasets. Bringing together such a range of datasets provides a geoscientific basis by which to estimate temperature in regions where direct observations are not available. Furthermore, the National Computational Infrastructure (NCI) is enabling insights into the nature of Australia's geothermal resources that had not been previously available.

Heat flow data across Australia are sparse, with around 150 publicly-available data-points. The heat flow data are unevenly distributed and mainly come from studies undertaken by the Bureau of Mineral Resources (BMR) and the Research School Earth Sciences at the Australian National University in the 1960s and 1970s. Geoscience Australia has continued work started under the federally-funded Onshore Energy Security Program (OESP), collecting data to add to the heat flow coverage of the continent. This report presents temperature, natural gamma and thermal conductivity data for eight boreholes across Australia. Temperature logging was performed down hole with temperatures recorded at intervals less than 20 cm. Samples of drill core were taken from each well and measured for thermal conductivity at Geoscience Australia. One dimensional, conductive heat flow models for the boreholes are presented here. These new determinations will add to the 53 already released by Geoscience Australia under the OESP, totalling 61 determinations added to the Australian continental heat flow dataset since 2007.

The Australian Geothermal Association compiled data on the installed capacity of direct-use geothermal and geoexchange systems in Australia, including large-scale ground source heat pumps and hot sedimentary applications through to December 2018. Large-scale direct-use hot sedimentary aquifer systems includes systems to heat swimming pools or provide hydronic heating systems. In geoexchange systems, the Earth acts as a heat source or a heat sink, exploiting the temperature difference between the surface (atmosphere) and at depth. The temperature of the Earth just a few metres below the surface is much more consistent than atmospheric temperature, especially in seasonal climates. These resources do not require the addition of geothermal heat.

<div>The lithology, geochemistry, and architecture of the continental lithospheric mantle (CLM) underlying the Kimberley Craton of north-western Australia has been constrained using pressure-temperature estimates and mineral compositions for &gt;5,000 newly analyzed and published garnet and chrome (Cr) diopside mantle xenocrysts from 25 kimberlites and lamproites of Mesoproterozoic to Miocene age. Single-grain Cr diopside paleogeotherms define lithospheric thicknesses of 200–250 km and fall along conductive geotherms corresponding to a surface heat flow of 37–40 mW/m 2. Similar geotherms derived from Miocene and Mesoproterozoic intrusions indicate that the lithospheric architecture and thermal state of the CLM has remained stable since at least 1,000 Ma. The chemistry of xenocrysts defines a layered lithosphere with lithological and geochemical domains in the shallow (&lt;100 km) and deep (&gt;150 km) CLM, separated by a diopside-depleted and seismically slow mid-lithosphere discontinuity (100–150 km). The shallow CLM is comprised of Cr diopsides derived from depleted garnet-poor and spinel-bearing lherzolite that has been weakly metasomatized. This layer may represent an early (Meso to Neoarchean?) nucleus of the craton. The deep CLM is comprised of high Cr2O3 garnet lherzolite with lesser harzburgite, and eclogite. The peridotite components are inferred to have formed as residues of polybaric partial mantle melting in the Archean, whereas eclogite likely represents former oceanic crust accreted during Paleoproterozoic subduction. This deep CLM was metasomatized by H2O-rich melts derived from subducted sediments and high-temperature FeO-TiO2 melts from the asthenosphere.</div><div><br></div><div>Geoscience Australia’s Exploring for the Future program provides precompetitive information to inform decision-making by government, community and industry on the sustainable development of Australia's mineral, energy and groundwater resources. By gathering, analysing and interpreting new and existing precompetitive geoscience data and knowledge, we are building a national picture of Australia’s geology and resource potential. This leads to a strong economy, resilient society and sustainable environment for the benefit of all Australians. This includes supporting Australia’s transition to net zero emissions, strong, sustainable resources and agriculture sectors, and economic opportunities and social benefits for Australia’s regional and remote communities. The Exploring for the Future program, which commenced in 2016, is an eight year, $225m investment by the Australian Government.</div><div><br></div><div><strong>Citation:</strong></div><div>Sudholz, Z.J., et al. (2023) Mapping the Structure and Metasomatic Enrichment of the Lithospheric Mantle Beneath the Kimberley Craton, Western Australia,&nbsp;<em><i>Geochemistry, Geophysics, Geosystems</i>,</em>&nbsp;24, e2023GC011040.</div><div>https://doi.org/10.1029/2023GC011040</div>