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A Multi-stage inversion framework for dynamic fracture characterization and long-term thermal performance prediction in an Enhanced Geothermal System
  • Kun Zhang,
  • Hui Wu
Kun Zhang
Peking University
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Hui Wu
Peking University

Corresponding Author:[email protected]

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Fractures play important roles in fluid and heat flow during heat extraction from an enhanced geothermal system (EGS). Quantifying the associated uncertainties in fractures is critical for predicting long-term thermal performance of EGSs. Considerable advancements have been made regarding the inversion of fracture characteristics such as aperture distribution. However, most previous studies assumed a constant fracture aperture to simplify the inversion, while both experimental and numerical results indicated significant variations in fracture aperture due to complex thermo-hydro-mechanical (THM) coupled processes during heat extraction. This study introduces a multi-stage inversion framework that integrates the Ensemble Smoother with Multiple Data Assimilation (ES-MDA) with a THM coupled model to capture the dynamic evolution of fracture aperture. The framework executes multiple aperture inversions at different times during EGS operation. In each inversion stage, we use ES-MDA to invert for fracture aperture by assimilating tracer data, and then perform THM modeling to analyze fracture aperture evolution under coupled THM processes and predict thermal performance. We propose a principle to assure a smooth transition between two consecutive inversion stages, that the posterior aperture fields obtained in an inversion stage are used as the prior aperture fields for the following stage, and the temperature field simulated in the previous inversion stage serves as the initial temperature field for the following stage. Application of the framework to a synthetic field-scale EGS model demonstrates its efficacy in capturing the dynamic evolution of fracture aperture, resulting in more accurate thermal predictions compared with previous inversion methods assuming constant fracture aperture.
06 Jan 2024Submitted to ESS Open Archive
21 Jan 2024Published in ESS Open Archive