We have studied possibilities to utilize the 1.4 km deep Pyhsalmi mine as a source of geothermal energy. Measured thermal conductivities of the Precambrian (1.9 Ga) crystalline bedrock hosting the massive Cu-Zn sulphide deposit vary between 2.5 and 3.5 W/mK, depending on the rock type, and the bedrock temperature increases with depth by 12–14 K/km. The design concept for heat utilization studied in this project is based on an underground borehole field exchanging heat between the bedrock and the water circulation loop, which then transfers thermal energy to the heat pumps. In the borehole heat exchanger (BHE) performance evaluations, we focused on a coaxial configuration, in which formation water circulates down in contact with borehole wall and returns inside a pipe. The borehole field modelled has a hemispherical geometry, so that all boreholes start from a central hall at the bottom of the mine (where the temperature is 21 C) and would be directed radially outwards. Our reference case consists of 136 boreholes having length of 300 m, thus covering a rock volume of 57 million cubic meters. Simulations indicate that this BHE fields can sustain heating power of 1 MW for at least 44 years, but the average temperature of the borehole field would decrease by about 10 degrees. Thermal power can be increased substantially by increasing the borehole density, but the lifetime of the BHE field decreases.

我们研究了利用 1.4 公里深的 Pyhsalmi 矿作为地热能源的可能性。根据岩石类型的不同，前寒武纪（1.9 Ga）结晶基岩的热导率在 2.5 到 3.5 W/mK 之间变化，基岩温度随深度增加 12-14 K/km。该项目研究的热利用设计理念是基于地下钻孔场在基岩和水循环回路之间进行热交换，然后将热能传递给热泵。在钻孔换热器 (BHE) 性能评估中，我们专注于同轴配置，其中地层水向下循环与钻孔壁接触并返回管道内。建模的钻孔场具有半球形几何形状，因此所有钻孔都从矿井底部的中央大厅（温度为 21 摄氏度）开始，并径向向外。我们的参考案例包括 136 个长度为 300 m 的钻孔，因此覆盖了 5700 万立方米的岩石体积。模拟表明，该 BHE 场可以维持 1 兆瓦的加热功率至少 44 年，但钻孔场的平均温度会降低约 10 度。通过增加钻孔密度可以显着增加热功率，但 BHE 场的寿命会减少。模拟表明，该 BHE 场可以维持 1 兆瓦的加热功率至少 44 年，但钻孔场的平均温度会降低约 10 度。通过增加钻孔密度可以显着增加热功率，但 BHE 场的寿命会减少。模拟表明，该 BHE 场可以维持 1 兆瓦的加热功率至少 44 年，但钻孔场的平均温度会降低约 10 度。通过增加钻孔密度可以显着增加热功率，但 BHE 场的寿命会减少。