Recent acquisition of deep crustal seismic and magnetotelluric data in the southern Northern Territory, in conjunction with current and previously completed studies, has led to an increased knowledge of the geological and geodynamic framework of the region. This improved understanding has been used to assess the potential for the presence of uranium and geothermal energy systems within the southern Northern Territory. Four uranium mineral systems were considered: sandstone-hosted, uranium-rich iron oxide-copper-gold, unconformity-related and magmatic-related. The analysis for uranium systems was undertaken in a 2D, GIS-based environment and employed a mineral systems approach consisting of four key components: 1) sources of metals, fluids and ligands, 2) drivers of fluid flow, 3) fluid flow pathways and architecture, and 4) depositional sites and mechanisms. Two geothermal systems were targeted: hot rock geothermal and hot sedimentary aquifer. For the assessment for hot rock geothermal systems, temperatures at depth were predicted in 3D using the 3D GeoModeller software package. Hot sedimentary aquifer potential was assessed using the modelled temperature at the basal contact of sedimentary basins containing favourable aquifer units.

Work 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. The Energy Initiative of the Federal Government, announced in August 2006, has restarted a geothermal project in GA. This paper outlines the scope of the Onshore Energy Security Program, the development and implementation of the new Geothermal Energy Project, and progress to date. The Onshore Energy Security Program A program to acquire pre-competitive geoscience information for onshore energy prospects has begun following the Prime Minister's Energy Security Initiative. The initiative provides $58.9 million over five years to Geoscience Australia for the acquisition of new seismic, gravity, geochemistry, heat flow, radiometric, magneto-telluric and airborne electromagnetic (EM) data to attract investment in exploration for onshore petroleum, geothermal, uranium and thorium energy sources. The program will be delivered in collaboration with the States and Territory under the existing National Geoscience Agreement. A set of principles have been developed to guide the program. According to the principles, proposed work must: promote exploration for energy-related resources, especially in greenfields areas; improve discovery rates for energy-related resources; be of national and/or strategic importance; and data acquisition must be driven by science. The program is structured with national-scale projects for each energy commodity (geothermal, petroleum, uranium and thorium) and for geophysical and geochemical acquisition. Regional scale projects in Georgetown-Isa, Gawler-Curnamona, Northern WA and the Northern Territory areas will assess the energy potential of those areas in detail. Other regions will be prioritised at a later stage of the OESP. Formulating the Geoscience Australia Geothermal Energy Project Based on consultation with State and Territory geological surveys and geothermal exploration companies, a list of the impediments faced by geothermal companies was identified. The Geothermal Energy Project addresses those that require geoscience input. The greatest geological problem facing explorers is a lack of understanding of the distribution of temperature in the upper crust of Australia. The two existing datasets that map temperature and heat distribution - the Austherm map of temperature at 5 km depth, and a database of heat flow measurements - both require a great deal of infilling. It is also possible to make predictive maps of expected heat based on geological models. These three ways of mapping heat, and the work that the project will do in each of these areas, is described in more detail in later sections. Other geoscience inputs that will help improve discovery rates and/or reduce risk to explorers and investors include a comprehensive and accessible geothermal geoscience information system, a better understanding of the stress state of the Australian crust, better access to seismic monitors during reservoir stimulation, and a Reserve & Resource definition scheme. Increasing the awareness of Australia's geothermal potential amongst decision makers and the general public may also help the funding of the development of the industry through Government support and investor confidence. The Geothermal Project has involvement in all of these activities, as outlined in later sections.

The Oceania region encompasses a range of geothermal environments and varying stages of geothermal development. Conventional geothermal resources in New Zealand, Papua New Guinea, Indonesia and the Philippines have been used for power generation for as long as 50 years, whereas Australia's non-conventional 'Hot Rock' geothermal resources have only recently been targeted as an energy source. New Zealand's geothermal resources are high-temperature convective hydrothermal systems associated with active magmatism, and these have been exploited for electricity generation since 1958. With a total installed capacity of ~445MWe, geothermal energy currently generates ~7% of New Zealand's electricity. This figure is likely to increase in response to the New Zealand Government's recent target of 90% of the country's electricity to be generated from renewable resources by 2025. Geothermal power plants used in New Zealand are either condensing steam turbines, or combined-cycle plants that utilise a steam turbine with binary units. In terms of energy consumed, direct-use of geothermal energy rivals electricity generation at approximately 10,000 TJ/yr. Applications include industrial timber drying, greenhouse warming and aquaculture, and may be stand-alone or cascading. Analogous high-temperature hydrothermal systems elsewhere in Oceania support installed electricity generation capacities of 56MWe in Papua New Guinea, 838MWe in Indonesia and 1931MWe in the Philippines. In contrast, Australia's geothermal plays are principally associated with high-heat-producing basement rocks. Typically these rocks are granites that are relatively enriched in the radioactive elements U, Th and K and thus have elevated heat generation (i.e. >6µW/m³). Elevated temperatures are found where this heat is trapped beneath sufficient thicknesses (>3km) of low-thermal-conductivity sediments. Low-temperature hydrothermal systems can be found in shallow aquifer units that overlie the hot basement. Hot Rock geothermal plays are typically found at greater depths (3 to 5km), where temperatures in the basement itself or in overlying sediments can exceed 250°C. Electricity can be generated from Hot Rock resources by artificially enhancing the geothermal system (e.g. increasing rock permeability at depth by hydro-fracturing). Although no electricity has yet been generated from Australia's Hot Rocks, a listed company (Geodynamics Ltd) has completed two 4200m-deep wells in the Cooper Basin, and expects to establish a 1MWe pilot plant by late-2008, a 50MWe plant by 2012, and 500MWe by 2015. As of January 2008, there are 33 companies in Australia prospecting for Hot Rock and hydrothermal resources, across 277 license-application areas that cover 219,00km². In support of industry exploration, and to increase uptake of geothermal energy in Australia, Geoscience Australia is currently compiling and collecting national-scale geothermal datasets such as crustal temperature and heatflow.

The Habanero Engineered Geothermal System (EGS) in central Australia has been under development since 2002, with several deep (more than 4000 m) wells drilled into the high-heat-producing granites of the Big Lake Suite to date. Multiple hydraulic stimulations have been performed to improve the existing fracture permeability in the granite. The 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 since 2008, to evaluate the fluid residence time in the reservoir alongside other hydraulic properties, and to provide comparative information to assess the effectiveness of the hydraulic stimulations. The closed-system and discrete nature of this engineered geothermal reservoir provides a unique opportunity to explore the relationships between the micro-seismic, rock property, production and tracer data. The most recent inter-well tracer test occurred 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. Sampling of the production fluids from H-4 occurred throughout the duration of the 3-month closed-circulation test. After correcting for flow hiatuses (i.e. interruptions in injection and production) 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. Applying moment analysis to the data indicated that approximately 56% of the tracer was returned during the circulation test (vs. approximately 70% from the 2008 H-1/H-3 tracer test). This suggests that a considerable 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. Flow capacity:storage capacity plots derived from the H-1/H-4 tracer test indicate that the Habanero reservoir is moderately heterogeneous, with approximately half of the flow travelling via around 25% of the pore volume. The calculated inter-well swept pore volume was approximately 31,000 m³, which is larger than that calculated for the H-1/H-3 doublet (~20,000 m³). This is consistent with the inferred increase in reservoir volume following hydraulic stimulation of H-4.

As part of the Onshore Energy and Security Program Geoscience Australia are producing regional geothermal energy assessments. The initial assessment (Huston, 2010) was conducted in the North Queensland region with a further assessment to be completed in the Gawler-Curnamona region, South Australia. The assessments, which incorporate geological, geophysical, geochemical and rock property data, identify geographic regions of high prospectivity for Hot Rock (HR) and Hot Sedimentary Aquifer (HSA) systems. The North Queensland assessment, consisting of a map of HR and HSA potential ranked from high to low was produced using GIS techniques. A heat production layer of polygons ranked from high to low was generated from solid geology maps and geochemical data. Heat production values for the lithologies were calculated using concentrations of radiogenic elements (U, K and Th). A thermal resistance ranking layer was produced by integrating thermal conductivity data with sediment thickness data. A temperature availability ranking layer was also generated based on the predicted temperature at 5 km using AUSTHERM07 database. The ranked layers were weighted based on their prospectivity potential and in conjunction with data uncertainty rankings,combined in the GIS to produce the final HR prospectivity map. To produce the HSA prospectivity map, aquifer thickness and water temperature ranking layers were added to the HR assessment.

Educational factsheet summarising geothermal systems (hydrothermal and Hot Rock systems), advantages of geothermal power generation in Australia, geothermal power generation systems, and future electricity generation in Australia using geothermal energy. The mini-abstract on the factsheet is as follows: Geothermal energy is the heat contained within the Earth and it can be used to generate electricity by utilising two main types of geothermal resources. Hydrothermal resources use naturally-occurring hot water or steam circulating through permeable rock, and Hot Rock resources produce super-heated water or steam by artificially circulating fluid through the rock. Electricity generation from geothermal energy in Australia is currently limited to an 80kW net power plant at Birdsville in south west Queensland. However this is likely to change in the future as Hot Rock power plants become increasingly commercially viable.

Educational factsheet discussing geothermal induced seismicity, what it is, why it happens, potential risks and mitigation strategies. Short abstract from factsheet header below: Hot Rock geothermal power production relies on using buried hot rocks to heat water and generate electricity. Australia is thought to have an enormous geothermal resource, capable of providing low-emission, cost-competitive energy for centuries to come. The nature of most Hot Rock resources in Australia necessitates artificial enhancement of the resources to make them viable for geothermal power production. One possible hazard associated with developing geothermal resources is induced seismicity. Induced seismicity is the term used to describe earthquakes generated by human activities. Induced earthquakes are associated with the movement of material into or out of the earth, for example during water reservoir filling, underground mining, and development of Hot Rock reservoirs. Exploration for geothermal energy in Australia has rapidly increased over the last five years, and geothermal exploration leases have been taken out around Melbourne, Adelaide, Hobart and Geelong. If shown to have viable geothermal resources, geological enhancement of these areas for Hot Rock power production may generate induced seismicity. However, experience in Australia to date suggests that the risks associated with geothermal induced seismicity are very low compared to that of natural earthquakes, and can be reduced by careful management and monitoring.

Extended abstracts from various authors compiled as the Proceedings volume of the 2012 Australian Geothermal Energy Conference, 14-16 November 2012, Crown Plaza, Coogee Beach, Sydney.

Extended abstract describing metallogenic significance of georgina-Arunta seismic line. The abstract discusses mainly the Neoproterozoic and Phanerozoic mineral potential, including implications to U, Cu-Co, Au, Cu-U and energy.

A regional seismic survey in north Queensland, with acquisition paremeters set for deep crustal imaging, show a potential geothermal target beneath about 2 km of sediments. Beneath the sedimentary structure there appears to be an area of low seismic reflection signal from about 1 s to 4 s. Combined with the relatively low gravity signature over this location, this area of low seismic reflection signal could be interpreted as a large granite body, overlain by sediments. This body lies near an area of high crustal temperature and suggests a potential geothermal energy target.