Design and optimization of the U-shaped well geothermal systems for heat production performance: A case study from Huangling, China

Abstract

U-shaped well geothermal systems have obvious advantages in deep geothermal development due to the long heat exchange distance and no fluid leakage. Well layout is a primary optimization target to enhance the heat production performance. However, there is a lack of studies for well location selection and installation configuration considering regional groundwater flow. In this study, a coupled thermo-hydro model considering 1D U-shaped well and 3D reservoirs groundwater flow is proposed for the optimization of U-well geothermal systems. The proposed model is calibrated by the field test of U-shaped well in Huangling, China. First, the U-shaped well geothermal system with multiple injection wells is designed. The feasibility is comprehensively evaluated from the aspects of heat production performance and levelized cost of electricity. Subsequently, the influence of groundwater flow on heat production performance is analyzed in detail, including flow velocity, porosity, aquifer thickness and flow direction. Finally, sensitivity studies of thermal conductivity of cement, wellbore diameter, and injection flow rate are investigated to provide reference for production operations. The results show that the heat production performance of the U-shaped well geothermal system with multiple injection wells are significantly better than the single U-shaped well. And the levelized cost of energy can be reduced by 0.0288 $/kWh compared to the average industrial electricity price in China. The groundwater flow velocity remarkably affects the heat production performance. The large aquifer thickness and porosity contribute to the improvement of the heat production performance of the U-shaped well geothermal system. The U-shaped well with injection wells located in the lower reaches of groundwater flow field has better heat production performance. The research results can provide references for design and optimization of the U-shaped well geothermal systems.