| Abstract |
Research over the last 10 years has indicated that Australia has a significant geothermal energy resource. Regions of high crustal temperature at depths 5km may be economic targets for hot dry rock technology. A new database of temperature measurements made in 5722 wells across Australia has been used to construct improved maps of the spatial distribution of temperature in the Australian crust. The new database, Austherm04, builds upon the earlier work of Somerville et al. (1994) by greatly improving data quality control and by including temperature data from a further 1430 wells. Whilst there has been some enhancement of the overall spatial coverage when compared with the earlier work, the bulk of the new data are still largely clustered within the same provinces that dominate the Somerville et. al. dataset. As a result, data distribution across the continent still tends to be rather patchy and irregular with some regions well represented and others not. An Arc/Info GIS coverage has been built from the Austherm04 database. This coverage was intersected with GIS grids (constructed from Australian mean surface temperature data provided by the Australian Bureau of Meteorology and depth to basement estimates provided by Geoscience Australia) to interpolate the mean surface temperature and depth-to-basement for each well location. Calculations of the crustal temperature at a depth of 5 kilometres at each well location were then made using measured or estimated thermal gradients, the surface temperature estimates and the depth to basement information. In the absence of specific data, a uniform gradient of 25?C/km was assumed for basement rocks. The calculated crustal temperatures at 5 km depth were used to interpolate grids of cell size equal to 0.02 degrees. Interpolation was performed across the continental dataset using geostatistical 'kriging. A variety of semivariogram error-modelling approaches have been tested. To date best results have been obtained with an exponential model. The crustal temperature maps produced in this study reveal large spatial variations in temperature across continental Australia. Lowest temperatures occur where basement is exposed at the surface such as in the Yilgarn Block, Gawler Craton and Lachlan Fold Belt. High temperatures are associated with thick sedimentary basin cover and the inferred presence of high heat production granites under the sedimentary sequences. Particular examples include the Cooper-Eromanga, Macarthur and Canning Basin regions. Other smaller areas of relatively elevated crustal temperature that may represent future hot dry rock targets include parts of the Sydney, Perth and Murray Basins. Whilst representing significant improvements over the previous Somerville et al. map, the new crustal temperature maps continue to be influenced by artefacts caused by the strongly heterogeneous spatial distribution of the subsurface temperature data across continental Australia. More sophisticated geostatistical methods and analysis on a province by province basis may offer some improvements but further temperature exploration data will probably be required to significantly improve the resource analysis. |