Performance enhancement, economic analysis, and futuristic insight of single-well medium-deep and deep geothermal systems

Geothermal energy, recognized for its sustainability and high capacity factor, offers a stable and renewable alternative to fossil fuels. However, conventional multi-well enhanced geothermal systems (EGS) face challenges such as high drilling costs, induced seismicity, and fluid loss. Single-well systems have emerged as a promising solution, eliminating the need for reinjection wells and reducing environmental risks. Despite their advantages, these systems are limited by low heat transfer efficiency in geological formations, hindering widespread commercial deployment.

This review, authored by Ang Li, R.S. Anand, Wenbo Huang, Juanwen Chen, Zhibin Li, Jian Guo, Qingshan Ma, and Fangming Jiang from the Chinese Academy of Sciences and the University of Science and Technology of China, was published in Frontiers in Energy. The study systematically examines performance enhancement and economic aspects of single-well systems for medium-deep and deep geothermal energy extraction.

The article highlights two main single-well configurations: coaxial downhole heat exchangers (CDHE) and super-long gravity heat pipes (SLGHP). While CDHE relies on pumped single-phase fluid, SLGHP utilizes phase-change heat transfer and gravity-driven flow, achieving over 1 MW of heat extraction without pumping. The thermal resistance of SLGHP has been decreased to approximately 10⁻⁵ to 10⁻⁶ K/W. Key enhancement strategies are analyzed, including increasing heat transfer area via horizontal or multilateral wells, improving the heat transfer coefficient using high-conductivity materials, and maximizing temperature differences through low-boiling-point fluids.

Economic analyses indicate that SLGHP systems, especially when retrofitted in abandoned wells, offer lower levelized energy costs (0.163 $/kWh for SLGHP vs. 0.374 $/kWh for CDHE). Multilateral well designs further improve economic efficiency by enhancing heat output relative to drilling costs. These findings underscore the potential of optimized single-well systems to provide sustainable and cost-effective geothermal energy, supporting global carbon neutrality efforts.

Original source:

https://link.springer.com/article/10.1007/s11708-024-0971-3

https://journal.hep.com.cn/fie/EN/10.1007/s11708-024-0971-3

Shareable link: https://rdcu.be/eSrOS

Keywords:

borehole heat exchanger / coaxial downhole heat exchangers / geothermal energy exploitation / single-well system / super-long gravity heat pipe