| Title | The effect of a temperature-dependent permeability limit on the convective upflow and temperature in a numerically modelled geothermal system |
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| Authors | D.Banerjee, D. Dempsey, D. Cusack, J. Hewett, B. Kennedy, J. Cater |
| Year | 2025 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | Brittle-ductile, flow, temperature-dependent permeability, convection, geothermal |
| Abstract | High-temperature (>220 °C) geothermal fields within the Taupo Volcanic zone (TVZ) are among the most promising resources for clean energy production and present a significant opportunity for sustainable energy development. An emerging frontier is the exploitation of geothermal fluids at superhot or supercritical temperatures higher than 350°C. In this work, numerical simulations of geothermal convection cells are used to investigate how thermal and physical rock properties influence heat transfer and geothermal accessibility at supercritical conditions. The focus of this work is the influence of thermally controlled brittle-ductile transition on the permeability properties of rock, that reduces fluid transport below a threshold temperature value. A range of convection cell scenarios has been investigated with varying circulation depth, Brittle-Ductile Transition (BDT) temperature range, and permeability anisotropy. For a BDT across the range 340 to 440°C, the estimated temperatures in convection cells at a depth of 2 km exceeded the highest recorded TVZ temperatures (340°C). As flow was permitted at progressively higher temperatures, shallow temperatures reached those consistent with supercritical wells in Krafla, Iceland. These preliminary results suggest that, to be consistent with New Zealand geothermal characteristics, heat transfer is likely to be conduction-dominated at supercritical temperatures and depths. However, future analysis of alternative mechanisms of permeability creation and loss, improved descriptions of temperature varying fluid properties, and better models of shallow permeability under transient simulations may require that we revisit this finding. |