Heat Propagation in High-Temperature Geothermal Wells : Analysis of temperature distribution in formations surrounding geothermal wells using numerical methods, along with the effects and mitigation strategies

Sammanfattning

This study investigates heat propagation patterns around high­temperature wells in advanced geothermal systems located in Näsudden, Gotland, through numerical analysis. It focuses on two­dimensional conduction heat transfer within the rock formation while also considering convection from both the well and the ambient air as boundary conditions. Key parameters such as thermal conductivity, specific heat capacity, density, porosity, and the convective heat transfer coefficient are included to represent subsurface conditions. The simulation results indicate a worst­case scenario of temperature increase over 30 years of operation, with an average surface temperature rise of 11◦C. At a distance of 24 meters from the well, surface temperatures could reach up to 70◦C, posing risks to soil biology and local ecosystems. Long­term temperature increases exceeding 5◦C may disrupt the natural groundwater­surface water cycle. To mitigate these impacts, strategies such as installing casings and utilizing cement are recommended to limit heat propagation. This research also shows that one layer of casing and cement can reduce the affected distance by approximately 7­10 meters closer to the well. Sensitivity analyses further reveal differences in heat propagation across various sedimentary rocks and the influence of fluid temperature changes on the distribution of ground temperatures. The result is that sandstone exhibits the most significant and extensive heat propagation compared to other sedimentary rocks. These findings are crucial for feasibility studies and the implementation of advanced geothermal systems.