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<p>This study develops a 3D full-scale COMSOL Multiphysics model to optimize heat extraction in single-well coaxial geothermal systems. Simulations demonstrate that enlarged annular space (0.255&#xa0;m outer/0.101&#xa0;m inner diameters) significantly enhances short-term performance. Mechanistic analysis further confirms that annular expansion increases thermal contact area by 3–25% across configurations. Specifically, it achieves a peak extraction rate of 3769.33&#xa0;kW, representing a 3.82% increase over the lowest-output Scheme 3 (3630.2&#xa0;kW) through expanded fluid-rock contact. Nevertheless, tube geometry sensitivity diminishes over time, resulting in merely 2% performance variance after 30&#xa0;years due to near-wellbore heat depletion and conductive dominance from deeper formations. Notably, turbulent water injection (40 m<sup>3</sup>/h in 0.252&#xa0;m/0.101&#xa0;m tubing) yields 13-fold higher cumulative heat extraction than CO<sub>2</sub>, establishing water as the optimal working fluid. Collectively, these findings indicate that transient optimization focusing on annular-turbulence synergy for immediate gains while accommodating long-term geological constraints enables sustainable geothermal exploitation. Consequently, this work provides design guidelines balancing short-term efficiency with reservoir sustainability for deep geothermal applications.</p>

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Numerical study on heat extraction performance and parameter optimization of single-well coaxial geothermal system

  • 期刊论文

  • 出版模式：

    开放获取

  • 发表日期：

    2026年3月4日

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  • Dandan Wang,
  • Xiong Wu,
  • Zhiwei Dang,
  • Huiming Fang,
  • Zhewei Shi,
  • Chao Huo

摘要

This study develops a 3D full-scale COMSOL Multiphysics model to optimize heat extraction in single-well coaxial geothermal systems. Simulations demonstrate that enlarged annular space (0.255 m outer/0.101 m inner diameters) significantly enhances short-term performance. Mechanistic analysis further confirms that annular expansion increases thermal contact area by 3–25% across configurations. Specifically, it achieves a peak extraction rate of 3769.33 kW, representing a 3.82% increase over the lowest-output Scheme 3 (3630.2 kW) through expanded fluid-rock contact. Nevertheless, tube geometry sensitivity diminishes over time, resulting in merely 2% performance variance after 30 years due to near-wellbore heat depletion and conductive dominance from deeper formations. Notably, turbulent water injection (40 m3/h in 0.252 m/0.101 m tubing) yields 13-fold higher cumulative heat extraction than CO2, establishing water as the optimal working fluid. Collectively, these findings indicate that transient optimization focusing on annular-turbulence synergy for immediate gains while accommodating long-term geological constraints enables sustainable geothermal exploitation. Consequently, this work provides design guidelines balancing short-term efficiency with reservoir sustainability for deep geothermal applications.