Performance comparison of different well configurations for medium-deep coaxial closed-loop geothermal systems

Abstract

Coaxial closed-loop geothermal systems are gaining prominence for medium-deep geothermal resource exploitation due to their small land footprint and stable heat extraction capability. Addressing the limitations of existing research, which primarily focuses on vertical systems, overlooks formation heterogeneity, and lacks a systematic comparison of well configurations, this study innovatively develops a two-dimensional transient heat transfer model that considers heterogeneous geological formations. For the first time, a comprehensive comparison of the heat extraction and economic performance of vertical, L-shaped, and multilateral coaxial closed-loop geothermal systems under short-term and long-term operation is conducted using a combination of theoretical analysis and Fluent-based numerical simulation. Results indicate that multilateral wells significantly enhance overall performance by increasing well spacing and reservoir contact area. At a mass flow rate of 3 kg/s, the heat extraction per meter of the multilateral well is 28.56 % and 34.11 % higher than that of the L-shaped and vertical wells, respectively, enhancing the system coefficient of performance (COP) by 1.13 % and 1.79 %, respectively. Furthermore, the profits are approximately 79.28 % and 169.84 % higher. Therefore, multilateral wells offer the greatest long-term benefits, followed by L-shaped wells, and finally vertical wells. This study provides a valuable reference for comprehensive evaluation and optimized design of coaxial closed-loop geothermal systems.