Hot Rocks
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An extension of previously developed methods to calculate in-situ 3D temperature directly from 3D geology models in 3D GeoModeller software now allows for quantification of the uncertainty associated with those calculations. This work is being collaboratively undertaken by Intrepid Geophysics and Geoscience Australia, and will offer Australia's geothermal industry both: i) a new predictive tool helping to reduce the risk of Enhanced Geothermal System (EGS) exploration and heat resource estimation, and ii) stochastic temperature and heat flow maps of Australia.
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The hot rock geothermal model in the Australian context comprises high-heat producing granites overlain by thick accumulations of low-thermal conductivity sediments. The granites have low concentrations of radiogenic elements, and over hundreds of millions of years, these elements decay and produce heat. The passage of this heat to the Earth's surface via upwards conduction is slowed by layers of sediments that have low thermal conductivity, creating 'hot spots' beneath the blankets. This thematic map shows granites attributed by heat production and basin depth. The majority of the granites depicted are of surface outcrop. The presence of high-heat producing granites adjacent to deep sedimentary basins may be used as a first-order indicator of where to further investigate the possibility of hot rock geothermal plays. The main frame of the map shows all granites (attributed by calculated heat production - where available), sedimentary basins (and their order e.g. where one basin is overlapped by another) and geothermal licences and applications. The top right inset map shows only those granites with a calculated radiogenic heat generation of >5 uW -3, with the depth of the sedimentary basins. This map provides a rapid view of areas that may be expected to have the greatest hot rock potential. The second-from-top inset map shows all suitable geochemical analyses from OZCHEM, attributed by calculated radiogenic heat generation. This shows both the distribution of data that goes into attributing the granite polygons, and also analyses of granites (and other rocks) that fall outside the mapped granite polygons that are otherwise excluded from the main map. The third-from-top inset map shows the distribution of drillholes with temperature measurements. The bottom inset map shows an image of the Austherm07 database, which is derived from the drillhole temperature information. The image shows the projected temperature of the crust at a depth of 5 kilometres, interpolated between the drillholes. Overlain on this image is the small number of publicly-available heat flow data.
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This is a 3 minute movie (with production music), to be played in the background during the October 28th 2010 Geoscience Australia Parlimentary Breakfast. The video shows a wide range of the types of activities that GA is involved in. These images include GA people doing GA activities as well as some of the results of offshore surveys; continental mapping; eath monitoring etc. The movie will be played as a background before and after GA's CEO (Chris Pigram) presentation.
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The hot rock geothermal model in the Australian context comprises high-heat producing granites overlain by thick accumulations of low-thermal conductivity sediments. The granites have low concentrations of radiogenic elements, and over hundreds of millions of years, these elements decay and produce heat. The passage of this heat to the Earth's surface via upwards conduction is slowed by layers of sediments that have low thermal conductivity, creating "hot spots" beneath the blankets. This thematic map shows granites attributed by heat production and basin depth. The majority of the granites depicted are of surface outcrop. The presence of high-heat producing granites adjacent to deep sedimentary basins may be used as a first-order indicator of where to further investigate the possibility of hot rock geothermal plays. The main frame of the map shows all granites (attributed by calculated heat production where available), sedimentary basins and their order (e.g. where one basin is overlapped by another) and geothermal licenses and applications. The top right inset map shows only those granites with a calculated radiogenic heat generation of >5 Wm-3, and the depths of the sedimentary basins. This map provides a rapid view of areas that may be expected to have the greatest hot rock potential. The second-from-top inset map shows all suitable geochemical analyses from OZCHEM, attributed by calculated radiogenic heat generation. This shows both the distribution of data that goes into attributing the granite polygons, and also analyses of granites (and other rocks) that fall outside the mapped granite polygons and are otherwise excluded from the main map. The third-from-top inset map shows the distribution of drillholes that have temperature measurements. The bottom inset map shows an image of the Austherm07 database, which is derived from the drillhole temperature information. The image shows the projected temperature of the crust at a depth of 5km, interpolated between the drillholes. Overlain on this image is the small number of publicly-available heat flow data. This map is GA GeoCat record 65306. ISBN (print): 978-1-921236-44-0; ISBN (web): 978-1-921236-45-7. Webpage: http://www.ga.gov.au/minerals/research/national/geothermal/index.jsp.
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Australia's emergent geothermal energy industry is growing rapidly. So far, 29 companies have applied for geothermal exploration licenses. The majority of these companies are prospecting for Hot Rock geothermal resources for electricity generation, with some companies targeting hydrothermal resources. The Hot Rock model in the Australian context comprises a thick sequence (>3km) of low-thermal conductivity sediments overlying deeper high-heat-producing granites. Until now, the key dataset available to industry to guide their geothermal exploration has been a map of crustal temperature at 5km depth1. Compiled from temperature measurements made in 5,722 petroleum wells across Australia, the map indicates a vast geothermal resource. Additional national-scale geothermal datasets are either incomplete, not publicly accessible, or have not been collected. In August 2006, the Australian Government announced an Energy Security Initiative. It provides $58.9M to Geoscience Australia (the national geoscience and spatial information agency) over five years for an Onshore Energy Security Program (OESP). The OESP aims to better understand Australia's geological potential for onshore energy resources such as petroleum, uranium and geothermal, and includes the acquisition of new seismic, radiometric, heat-flow, magneto-telluric, gravity, magnetic, geochemical and drill-hole data. Providing new data will help attract company exploration in new areas by enhancing the chances of discovery and reducing the risks to investors. Established as part of the OESP, a new Geothermal Energy Project will generate precompetitive geoscientific information for geothermal explorers through two major activities: creating maps of heat distribution across Australia, and developing a geothermal information system. Heat distribution will be mapped in three ways: (1) new heat flow measurements in existing and new drill-holes; (2) a granite source-sediment heat trap map to identify Hot Rock systems; and (3) enhancements to the 5km-temperature-map method of Chopra and Holgate1. The geothermal information system will include thermal conductivity, thermal gradient, geochemistry, density, and heat production amongst other data types. The Australian Government is also facilitating and funding the preparation of a Geothermal Industry Development Framework, which is being lead by the Department of Industry, Tourism and Resources. The Development Framework aims to support the growth of Australia's geothermal industry by identifying opportunities and impediments to the industry's growth, and developing strategies to ensure that technical, economic and regulatory obstacles are tackled in a coordinated way. 1 Chopra, P. and Holgate, F., (2005) A GIS analysis of temperature in the Australian crust, Proceedings of the World Geothermal Congress 2005, Antalya, Turkey, 24-29 April 2005.
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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.
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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.
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The collection includes 17,247 measurements of temperature and temperature gradients collected down 5513 individual wells. This information formed the basis for the 'OZTemp Interpreted Temperature at 5km Depth' image of Australia <b>Value: </b>These observations are used to assess heat flow which can be used to infer deep geologic structure, which is valuable for exploration and reconstructions of Australia's evolution <b>Scope: </b>Nationwide collection corresponding to accessible boreholes and published measurements
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Like many of the basins along Australia's eastern seaboard, there is currently only a limited understanding of the geothermal energy potential of the New South Wales extent of the Clarence-Moreton Basin. To date, no study has examined the existing geological information available to produce an estimate of subsurface temperatures throughout the region. Forward modelling of basin structure using its expected thermal properties is the process generally used in geothermal studies to estimate temperatures at depth in the Earth's crust. The process has seen increasing use in complex three-dimensional (3D) models, including in areas of sparse data. The overall uncertainties of 3D models, including the influence of the broad assumptions required to undertake them, are generally only poorly examined by their authors and sometimes completely ignored. New methods are presented in this study which will allow estimates and uncertainties to be addressed in a quantitative and justifiable way. Specifically, this study applies Monte Carlo Analysis to constrain uncertainties through random sampling of statistically congruent populations. Particular focus has been placed on the uncertainty in assigning thermal conductivity values to complex and spatially extensive geological formations using only limited data. As a case study these new methods are then applied to the New South Wales extent of the Clarence-Moreton Basin. The geological structure of the basin has been modelled using data from existing petroleum drill holes, surface mapping and information derived from previous studies. A range of possible lithological compositions was determined for each of the major geological layers through application of compositional data analysis. In turn, a range of possible thermal conductivity values was determined for the major lithology groups using rock samples held by the NSW Department of Primary Industries (DPI). These two populations of values were then randomly sampled to establish 120 different forward models, the results of which have been interpreted to present the best estimate of expected subsurface temperatures, and their uncertainties. These results suggest that the Clarence-Moreton Basin has a moderate geothermal energy potential within an economic drilling depth. This potential however, displays significant variability between different modelling runs, which is likely due to the limited data available for the region. While further work could improve these methods, it can be seen from this study that uncertainties can provide a means by which to add confidence to results, rather than undermine it.
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A 3D map of the Cooper Basin region has been produced over an area of 300 x 450 km to a depth of 20 km (Figure 1). The 3D map was constructed from 3D inversions of gravity data using geological data to constrain the inversions. It delineates regions of low density within the basement of the Cooper/Eromanga Basins that are inferred to be granitic bodies. This interpretation is supported by a spatial correlation between the modelled bodies and known granite occurrences. The 3D map, which also delineates the 3D geometries of the Cooper and Eromanga Basins, therefore incorporates both potential heat sources and thermally insulating cover, key elements in locating a geothermal play. This study was conducted as part of Geoscience Australia's Onshore Energy Security Program, Geothermal Energy Project. This 3D data release constitutes the first version of the Cooper Basin region 3D map. A future data release (version 2 of the 3D map) will extend the area to the north and east to encompass the entire Queensland extension of the Cooper Basin. The version 2 3D map will incorporate more detailed 3D models of the Cooper and Eromanga Basins by delineating the major internal sedimentary sequences within the basins. Thermal properties will then be incorporated into the 3D map to produce a 3D thermal model. The goal is to produce a 3D thermal model of the Cooper Basin region that not only matches existing temperature and heat flow data in the region, but also predicts regions of high heat flow and elevated temperatures in regions where no heat flow or temperature data exists.