| Title | Thermal Thinking: Optimal Targeting for Australian Geothermal Explorers |
|---|---|
| Authors | Alexander Musson, Ben Harrison, Kate Gordon, Sarah Wright, Mike Sandiford |
| Year | 2009 |
| Conference | Australian Geothermal Energy Conference |
| Keywords | Australia, Latrobe Valley, heat flow modelling, heat refraction, palaeoclimatic corrections, Enhanced Geothermal Systems (EGS), Hot Fractured Rocks (HFR), Hot Dry Rocks (HDR), Deeply Buried Sedimentary Aquifers (DBSA), Hot Sedimentary Aquifers (HSA). |
| Abstract | The two foremost criteria that define the viability of a potential geothermal reservoir are: the highest temperature at the shallowest depth, and sustainable geofluid flow rates. In addressing the former, geothermal explorers face a difficult challenge; a challenge starting with scarce or inaccurate thermal datasets extracted mostly from shallow drillholes, and concluding with oversimplified interpretations and underconstrained thermal models. In the absence of deep drilling, temperature predictions at a target depth of several kilometers require the extrapolation of thermal data obtained from boreholes typically a few hundred metres deep. Because an uncertainty of 1 ºC at a 100 m depth translates to an error of 40 ºC at 4,000 m, it is essential that thermal data from shallow drillholes, in particular heat flow, be well constrained. Often the analysis of heat flow is considered as a one-dimensional steady-state and purely conductive heat transfer problem. This simplified view ignores transient effects and spatial variations which arise from heat and fluid transport as well as the inherent threedimensional heterogeneity and anisotropy of the geological subsurface. In this context our approach to the problem is to establish a more rigorous evaluation in assessing the nature and significance of primary data. We specifically explore the role of heat refraction and palaeoclimatic transients and its incidence on extrapolation methods. In certain circumstances primary data from shallow boreholes can be evaluated and adequately relied upon for extrapolation at target depth, independently of deep drilling. We propose conceptual models showing why heat refraction, heat insulation, rock anisotropy and palaeoclimate cannot be ignored and how consequently explorers can optimize their geothermal targets. |