Effect of Injection Rate on the Heat Exchange Process in EGS: Insights from Laboratory Experiments

Abstract The flow and heat transfer characteristics in the hot dry rock (HDR) fracture system are crucial for the efficient development of geothermal energy. To explore the influence of fluid leakage and the injection-production process on the long-term cycle of geothermal reservoirs during the heat exchange process, this work introduces the development of an in-situ system for HDR geothermal resources and conducts a large-scale physical simulation experiment of long-term injection-production flow and heat exchange using this system. This provides a simulation method for developing HDR geothermal resources. The study systematically analyzed fluid leakage, production pressure difference, production flow rate, production well exploitation temperature, and monitoring well temperature changes during low-temperature fluid injection. Additionally, it deeply explored the fluid recovery rate, the influence of heat exchange medium leakage on heat transfer performance, and the timing of these actions. The results indicate differences in fracture conductivity among various heat exchange channels during the process, leading to different factors affecting the heat exchange rate at different stages. During heat transfer, the exploitation temperature of the production well shows a downward trend, and higher flow rates result in faster declines. In the middle and late stages of injection-production heat transfer, the leakage channel activates under the combined effects of high osmotic pressure. The conductivity of the leakage channel gradually increases during the heat exchange process, severely affecting the long-term exploitation of geothermal resources.