| Title | Establishing Hot Rock Exploration Models: from Synthetic Thermal Modelling to the Cooper Basin 3D Geological Map |
|---|---|
| Authors | Tony Meixner, Stephen Johnston, Alison Kirkby, Helen Gibson, Ray Seikel, Kurt St |
| Year | 2009 |
| Conference | Australian Geothermal Energy Conference |
| Keywords | 3D map, thermal modelling, stochastic, Cooper Basin, high-heat producing granites, inversion modelling |
| Abstract | A large number of exploration models for Hot Rock geothermal energy plays in Australia are based on high-heat producing granites (HHPG) in combination with overlying low-conductivity sedimentary rocks providing the insulator necessary to accumulate elevated temperatures at unusually shallow (therefore accessible) depths. Unknowns in this style of geothermal play include the composition and geometry of the HHPG and its thermal properties and the thickness and thermal properties of the overlying sediments. A series of 3D geological models have been constructed to investigate the range of geometries and compositions that may give rise to prospective Hot Rock geothermal energy plays. A 3D geological map of the Cooper Basin region, which contains known HHPG beneath thick sedimentary sequences, and the Millungerra Basin region east of the Mt Isa Inlier, have been constructed from gravity inversions constrained by geological data. The inversion models delineate regions of low density within the basement that are inferred to be granitic bodies. Thermal forward modelling was carried out using GeoModeller software by assigning measured and estimated thermal properties to the mapped lithologies. An enhancement of the GeoModeller software allows input of thermal properties to be specified as distribution functions. Multiple thermal simulations were used to estimate the in-situ heat resource, thus reducing the exploration risk. The two thermal modelling techniques can be used as a predictive tool in regions where little or no temperature and geological data are available. A series of synthetic 3D maps were constructed using different granite geometries beneath varying thicknesses of cover sediments. The gravity, heat flow and vertical temperature gradients were forward modelled using typical density contrasts, heat production rates and thermal conductivities. Geothermal explorers in the Cooper Basin region can now use the results of the density modelling to identify the geometries and depth of burial of potential HHPG bodies, and also use the results of the thermal modelling to predict heat flows and temperature gradients associated with the bodies. |