Numerical simulation of temperature recovery process after enhanced geothermal system shutdown

doi:10.7523/j.ucas.2022.067

Abstract

Abstract: During the operation of the enhanced geothermal system (EGS), the temperature of the artificial reservoir in the hot dry rock (HDR) will rapidly decline, and the external heat supply will be unable to keep up with the system’s rate of heat extraction. At the same time, it will also have a significant impact on the artificial reservoir’s fluid pressure. The predecessors conducted extensive research on the temperature field and fluid pressure field changes during HDR exploitation process, but little attention has been paid to the temperature recovery process and fluid pressure field changes of artificial reservoirs after production has ceased, this process is critical for the site selection of new geothermal wells and the reuse of abandoned geothermal wells. The numerical simulation software COMSOL Multiphysics is used in this paper to establish a two-dimensional thermal-hydraulic coupling numerical model of the two-well EGS during operation and after shutdown, considering the contribution of radioactive heat generation and the influence of different thermal conductivities. According to the findings, heat convection is the primary mode of heat exchange during EGS operation, and the temperature of the artificial reservoir declines rapidly. The EGS has reached the end of its operational life after 19 years, while the artificial reservoir has lost its exploitation value after 68 years. The natural recovery process of artificial reservoir temperature lasts 10 000 years after geothermal exploitation is terminated. The primary technique of heat transfer and temperature recovery is conduction. The higher the thermal conductivity, the sooner the artificial reservoir temperature recovers.

Key words: hot dry rock (HDR), temperature recovery, heat conduction, thermal conductivity

CLC Number:

P315

LIU Hanqing, HU Caibo, ZHAO Guiping. Numerical simulation of temperature recovery process after enhanced geothermal system shutdown[J]. Journal of University of Chinese Academy of Sciences, 2024, 41(2): 222-230.

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