The complex thermal-hydraulic-mechanical (THM) coupling is the key issue to the energy extraction from a geothermal reservoir, where fractures are the main channels for fluid circulation and heat transfer. However, the effects of matrix deformation-induced aperture variation and fracture roughness on heat recovery efficiency are unclear. In this paper, a fully coupling THM model based on a discrete fracture network is proposed to explore these coupling effects. First, the fracture roughness and the fracture aperture variation with effective stress are introduced. Second, the water flow and heat transfer in the matrix and fractures as well as the deformation of the geothermal reservoir are individually formulated for a fractured geothermal reservoir. Third, the model is validated with analytical solution for its thermal-hydraulic (TH) coupling effect and literature data for its hydraulic-mechanical (HM) coupling effect. Finally, the features of heat transfer and fluid flow in the fractured geothermal reservoir are comparatively analyzed through four scenarios. The simulation results indicate that the discrete fracture network severely impacts the pressure distribution and temperature advance. The aperture variation induced by solid deformation can enhance heat transfer efficiency, and the fracture roughness can reduce the heat transfer efficiency.

中文翻译：

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具有离散裂缝网络的地热储层热力-水力-机械耦合研究

复杂的热-水-机械 (THM) 耦合是从地热储层提取能量的关键问题，其中裂缝是流体循环和传热的主要通道。然而，基体变形引起的孔径变化和断裂粗糙度对热回收效率的影响尚不清楚。在本文中，提出了一种基于离散裂缝网络的全耦合 THM 模型来探索这些耦合效应。首先，介绍了裂缝粗糙度和裂缝孔径随有效应力的变化。其次，对于裂缝性地热储层，基质和裂缝中的水流和传热以及地热储层的变形是单独制定的。第三，该模型通过其热-水 (TH) 耦合效应的解析解和其液压-机械 (HM) 耦合效应的文献数据进行了验证。最后，通过四种情景对比分析了裂缝性地热储层的传热和流体流动特征。模拟结果表明，离散裂缝网络严重影响压力分布和温度提前。固体变形引起的孔径变化会提高传热效率，而断裂粗糙度会降低传热效率。模拟结果表明，离散裂缝网络严重影响压力分布和温度提前。固体变形引起的孔径变化会提高传热效率，而断裂粗糙度会降低传热效率。模拟结果表明，离散裂缝网络严重影响压力分布和温度提前。固体变形引起的孔径变化会提高传热效率，而断裂粗糙度会降低传热效率。