Comparative investigation of the heat extraction performance of an enhanced geothermal system using H2, CO2, and H2O as working fluids

• Published in: Energy Geoscience Vol. 6; no. 3; p. 100429
• Main Authors: Wang, Dandan, Wu, Xiong, Zhao, Pu, Fang, Huiming, Dang, Zhiwei, Shi, Zhewei, Huo, Chao
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.09.2025; KeAi Communications Co., Ltd
• Subjects: COMSOL multiphysics; Enhanced geothermal system; Heat extraction performance; Single-well coaxial tube; Working fluid; Heat extraction performance; Single-well coaxial tube; Working fluid; Enhanced geothermal system; COMSOL multiphysics
• ISSN: 2666-7592; 2666-7592
• DOI: 10.1016/j.engeos.2025.100429

The optimization of working fluids in single-well coaxial geothermal systems presents a critical pathway for advancing the use of enhanced geothermal systems (EGS) in renewable energy applications. This study evaluates the thermo-hydraulic performance of three working fluids (H2O, CO2, and H2) in a single-well coaxial geothermal system, focusing on the effects of their injection temperatures. Using a 3D finite element model in COMSOL Multiphysics, simulations were conducted at three injection temperatures (17 °C, 27 °C, 40 °C) under constant mass flow rates. The results reveal that hydrogen significantly outperforms water and carbon dioxide, achieving a 297.77 % and 5453.76 % higher thermal output, respectively. Notably, the heat transfer efficiency is significantly improved when the injected working fluids are at 40 °C, compared to 27 °C; this demonstrates a positive correlation between injection temperature and thermal recovery. Though water systems exhibit better geological compatibility, the superior thermal properties of hydrogen position it as a promising alternative—despite potential subsurface challenges. This study provides critical insights for advancing the application of high-efficiency geothermal systems as well as the development of non-aqueous working fluids, thus contributing to the sustainable utilization of geothermal energy. [Display omitted] •Demonstration of hydrogen's 297.77 % thermal superiority over water in coaxial geothermal systems.•Identification of Hydrogen's transport advantage despite geological challenges versus H2O/CO2.•Multi-criteria optimization framework for next-generation EGS working fluids.