Within the Central Australian region, nominally constrained by 22.5oS 134oE and 31.5oS 144oE for this study, lie several systems of stacked basins beneath the extensive Mesozoic Eromanga Basin. Remnants of Proterozoic basins are largely inferred from gravity, unexplored, and are not everywhere differentiated from an extensive cover of the lower Palaeozoic Warburton Formation. This sequence is the central link between the contiguous Amadeus, Officer and Georgina Basins, and the Thomson Fold Belt. Since the Carboniferous, the region has largely experienced intracratonic sag and has accumulated continental sediments, including thick coal measures, with intermittent tectonism and uplift. In late Early Cretaceous, marine conditions briefly invaded this subsiding region, but continental sedimentation resumed in the Late Cretaceous. Tectonism occurred in the Tertiary with basin inversion and subsequent formation of the Great Artesian Basin. In the Cainozoic, the region is again in subsidence and accommodating fluvial and aeolian sediment slowly into the Eyre Basin. The preserved depocentres of the Carboniferous-Permian-Triassic Cooper, Pedirka-Simpson, and Galilee Basins are spatially separate, although all contain comparable, largely organically-mature continental coal measure sequences.

Work conducted at the Bureau of Mineral Resources (now Geoscience Australia) in the early 1990s was instrumental in bringing hot rocks geothermal research and development to Australia. Following the announcement of the Australian Government's Energy Initiative in August 2006, a new geothermal project has been started at Geoscience Australia. This paper, presented at 3rd Hot Rock Energy Conference in Adelaide, August 2007, outlines the scope of the Onshore Energy Security Program and the development, implementation and progress to date of the Geothermal Energy Project.

Currently it is difficult to assess the quality of Australian geothermal exploration targets, particularly for those with differing amounts of geological data. To rectify this, Geoscience Australia is developing a tool for evaluating geothermal potential across the continent and for identifying areas that warrant additional investigation. An important first step in the development of this tool is synthetic thermal modelling. Synthetic modelling has been used to perform a sensitivity analysis, determine the importance of different geothermal parameters and the values necessary to produce specific temperatures at depth. The results of this work are presented in this abastract.

The Habanero Enhanced Geothermal System (EGS) in central Australia has been under development since 2002, with several deep (more than 4000 m) wells drilled to date into the high-heat-producing granites of the Big Lake Suite. Multiple hydraulic stimulations have been performed to improve the existing fracture permeability in the granite. Stimulation of the newly-drilled Habanero-4 well (H-4) was completed in late 2012, and micro-seismic data indicated an increase in total stimulated reservoir area to approximately 4 km². Two well doublets have been tested, initially between Habanero-1 (H-1) and Habanero-3 (H-3), and more recently, between H-1 and H-4. Both doublets effectively operated as closed systems, and excluding short-term flow tests, all production fluids were re-injected into the reservoir at depth. Two inter-well tracer tests have been conducted: the first in 2008, and the most recent one in June 2013, which involved injecting 100 kg of 2,6 naphthalene-disulfonate (NDS) into H-1 to evaluate the hydraulic characteristics of the newly-created H-1/H-4 doublet. After correcting for flow hiatuses and non-steady-state flow conditions, tracer breakthrough in H-4 was observed after 6 days (compared to ~4 days for the previous H-1/H-3 doublet), with peak breakthrough occurring after 17 days. Extrapolation of the breakthrough curve to late time indicates that approximately 60% of the tracer mass would eventually be recovered (vs. approximately 80% for the 2008 H-1/H-3 tracer test). This suggests that a large proportion of the tracer may lie trapped in the opposite end of the reservoir from H-4 and/or may have been lost to the far field. The calculated inter-well swept pore volume is approximately 31,000 m³, which is larger than that calculated for the H-1/H-3 doublet (~20,000 m³). A simple 2D TOUGH2 tracer model, with model geometry constructed based on the current conceptual understanding of the Habanero EGS system, demonstrates good agreement with the measured tracer returns in terms of timing of breakthrough in H-4, and observed tracer dispersion in the tail of the breakthrough curve.

This report is a formal release of 12 new heat flow determinations made by Geoscience Australia. These new data are located in WA, NSW and Tasmania, and add to the 41 heat flow determinations previously released under the Onshore Energy Security Program.

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.

In Australia to date, there are only a handful of projects that have drilled deep wells to intersect geothermal reservoir targets, and limited flow tests have been performed. Consequently, the characteristics and behaviour of geothermal reservoirs in Australia (geometries, fluid chemistry, mineralogy, permeability type and distribution, temperature distribution etc.) are not well understood. It is clear that the geological variability in the geothermal plays targeted to date (and in the future) will result in diverse reservoir types, but regardless of setting, all geothermal reservoirs must have sufficient permeability to enable fluid flow and heat extraction. Geochemical tracers have been used internationally for many years to improve the understanding of reservoir dynamics in conventional geothermal systems. Their application in Australia is yet to be widely demonstrated however they provide an attractive opportunity to learn more about geothermal reservoirs in Australian geological settings. Tracers can be classified as either conservative or reactive, and can be used in liquid-phase, vapour-phase or two-phase reservoirs. Tracer tests can provide information on inter-well connectivity, fluid mean residence time, recharge areas, swept pore volumes, temperatures, fracture surface area, flow-storage capacity relationships and volumetric fluid sweep efficiencies. In addition, tracer data can be used with numerical transport codes to help validate 3D reservoir models. This paper presents an overview of existing tracers and their capabilities, and new research directions in tracer science internationally.

The economic viability of geothermal energy depends on the depth that must be drilled to reach the required temperature. This depends on the geothermal gradient, which varies vertically and horizontally in the Earth's crust. Traditionally these variations in geothermal gradient have been interpreted in terms of thermal conduction. However, advection and convection influence the temperature distribution in some sedimentary basins. Convection can cause the temperature gradient to vary significantly with depth, such that temperature estimates derived from extrapolation of shallow temperature gradients could be misleading. We use borehole temperature measurements in the Perth Basin (Western Australia) and the Cooper Basin (South Australia and Queensland) to reveal spatial variations in the geothermal gradient, and consider whether these patterns are indicative of convection.

A three-dimensional (3D) map of the Cooper Basin region has been produced from 3D inversions of Bouguer gravity data using geological data to constrain the inversions. The 3D map delineates regions of low density within the basement of the Cooper/Eromanga Basins that are inferred to be granitic bodies. This 3D data release constitutes the second version of the 3D map of the Cooper Basin region. It builds on Version 1 of the Cooper Basin Region Geological map, released in 2009. The Cooper Basin region is coincident with a prominent geothermal anomaly and forms part of a broad area of anomalously high heat flow. High-heat-producing granites, including granodiorite of the Big Lake Suite (BLS) at the base of the Cooper and Eromanga Basins sequences combined with thick Cooper/Eromanga sedimentary sequences that provide a thermal blanketing effect, result in temperatures as high as 270° C at depths <5 km. The location and characteristics of other granitic bodies are poorly understood and accurately identifying them is an important first step towards future geothermal exploration in this region. 3D Bouguer gravity field inversion modelling was carried out using the UBC inversion software. An initial gravity inversion was performed using seismic horizons to constrain the 3D distribution of the Cooper/Eromanga Basin sediments. Densities, derived from seismic velocities from a refraction seismic survey in the region, were assigned to the Cooper/Eromanga sediments in order to constrain their gravity contribution. A series of Iso-surfaces were generated, enclosing low density lobes within the basement of the initial sediment-constrained inversion model. Gravity 'worms' were used to pick the iso-surfaces that approximate the lateral sub-sediment extent of potential granites within the basement. A series of subsequent granite-constrained inversions were generated by assigning different maximum cut-off depths to the lobes. The inversion model that produced the most 'neutral' result had a maximum cut-off depth of 10 km. The 3D map was then used to predict temperatures throughout the volume of the map. Thermal properties were sourced from the literature and from direct measurements. Forward predictions of temperatures were carried out using the Simulator for HEat and MAss Transport (SHEMAT) software package. Thermal properties were iteratively updated until a satisfactory match was achieved between the model and temperature measurements. The resulting temperature distribution gives strongly elevated temperatures over the BLS, as well as broader regions of elevated temperature in the northwest of the study area toward Mt Isa, under the Adavale Basin in the north-east of the study area, and south-east of the BLS. Uncertainty was analysed using a stochastic modelling technique. A sensitivity analysis was first performed to select the parameters which, when varied, had the greatest effect on the predicted temperatures. These parameters are: thermal conductivity of the basin sediments, heat production of the basement and granite units, and basal heat flux. Stochastic models were then run, giving the standard deviation of the temperature at each point in the model. The resulting standard deviation distribution shows that areas of highest predicted temperature are also areas of highest error. However, when the standard deviation values are converted to percentage error, a different pattern emerges: Highest error values are observed where the Cooper Basin sediments are thickest. Lower error values are observed over the BLS and in the southeast of the model area.

Processed seismic data (SEG-Y format) and TIFF images for the 2007 Georgetown - Charters Towers Deep Crustal Seismic Survey (L185), acquired by Geoscience Australia (GA) under the Onshore Energy Security Program (OESP), in collaboration with the Queensland Geological Survey. Stack and migrated data for line 07GA-GC1 as well as CDP coordinates and maps. 07GA-GC1 is 492.9 km long. The traverse began at Ooralat Station, north of the Gulf Developmental Road and headed southeast toward Einasleigh along dirt roads. At Einasleigh, the line veered east-southeast in the direction of Charters Towers passing to the west of the township, then traversed through the Charters Towers gold mining area and terminated approximately 100 km south of Charters Towers at the Cape River. Raw data for this survey are available on request from clientservices@ga.gov.au