| Abstract |
Conventional geothermal settings are convective and advective in nature, related to heat transfer by the physical motion of fluids and steam within volcanic and shallow magmatic environments. Early EGS development in Europe has also encountered convective conditions. However, Australia is largely a conductive geothermal setting. The embryonic Australian geothermal sector has looked towards the established European and US geothermal sectors for learnings, but little attention has been paid to the distinctly different nature of heat transfer (convection versus conduction) in these settings and what this may mean for resource estimation. The Geothermal Reporting Code governs the declaration of Geothermal Resource estimates by public companies in Australia. Whilst the Code allows flexibility in the methods of estimation for an Inferred Geothermal Resource, the use of dynamic reservoir modeling methods at the resource estimation stage, as commonly applied in European and US geothermal provinces, is problematic where achievable fluid transmission rates are totally untested or, at best, poorly constrained. The conductive transfer of heat from the surrounding rocks is often of secondary importance in convective systems. In contrast, the use of stored heat methods to estimate an Inferred Resource should appropriately account for heat available in the geothermal systems within the Australian context. This paper compiles the outcomes of recent 3D numerical conductive heat flow modeling exercises undertaken for various commercial projects in Australia and presents a statistical analysis of Inferred Resource distributions for EGS and other projects. These projects tend to have large stored heat values (in-place petajoules) within a normal distribution. A sensitivity analysis of the variables used in the 3D models demonstrates the unique nature of conductive geothermal resources. |