Helen Gibson

Stochastic temperature, heat flow and geothermal gradient modeling direct from a 3D map of the Cooper Basin region, Central Australia

Significant volumes of Big Lake Suite granodiorite intrude basement in the Cooper Basin region of central Australia. Thick sedimentary sequences in the Cooper and overlying Eromanga Basins provide a thermal blanketing effect resulting in elevated temperatures at depth. 3D geological maps over the region have been produced from geologically constrained 3D inversions of gravity data. The inverted density models delineate regions of low density within the basement that are interpreted to be granitic bodies. The 3D maps include potential heat sources and thermally insulating cover, the key elements in generating an Enhanced Geothermal System (EGS) play. A region was extracted from the 3D geological map and used as a test-bed for modelling the temperature, heat flow and geothermal gradients. The test region was populated with thermal properties and boundary conditions were approximated. Temperatures were generated on a discretised version of the model within GeoModeller and were solved by explicit finite difference approximation using a Gauss-Seidel iterative scheme. The thermal properties that matched existing bottom hole temperatures and heat flows measurements were applied to the larger 3D map region. An enhancement of the GeoModeller software is to allow the input thermal properties to be specified as distribution functions. Multiple thermal simulations are carried out from the supplied distributions. Statistical methods are used to yield the probability estimates of the temperature and heat flow, reducing the risk of exploring for heat.

3D Geology, Temperature, Heat Flow And Thermal Gradient Modeling of the North Perth Basin, Western Australia

Summary Aiming to achieve an accurate steady state, 3D conductive heat flow model of the north Perth Basin, we first built a well-constrained 3D geology model and compiled bestavailable thermal conductivity and heat production rate data. A finite difference code implemented in the same software ( 3D GeoModeller ) enabled computation of 3D temperatures, heat flows, and geothermal gradients directly from the geology model. As well as direct visualization of the resulting 3D grids, we derived 2D grids including: i) temperature-maps of chosen depth horizons; ii) depth-maps of chosen isotherm surfaces; iii) a surface heat flow grid (draped to fit topography); and iv) vertical and horizontal temperature gradient-maps for chosen depth slices. This study has implications for geothermal energy exploration in Western Australia where the search for Enhanced Geothermal Systems (EGS) or direct-use heat plays begins with identification of anomalously high heat occurrences at accessibly shallow depths.

Reconciling high resolution airborne gravity gradiometry surveys with 3D mine geology models: Sensitivity testing and new approaches ready for greenfields exploration

GEM Chengdu 2015: International Workshop on Gravity, Electrical & Magnetic Methods and Their Applications Chengdu, China. April 19-22, 2015 *The corresponding author: des@intrepid-geophysics.com. Reconciling high resolution airborne gravity gradiometry surveys with 3D mine geology models: Sensitivity testing and new approaches ready for greenfields exploration D.J. FitzGerald*, Helen Gibson, and Matt Zengerer, Intrepid Geophysics