Abstract Our previous study ( Song et al., 2018 ) presented a novel enhanced geothermal system (EGS) with multilateral wells to exploit geothermal energy, and illustrated that the multilateral-well EGS had a better heat extraction performance than conventional double-well EGS. However, to further improve the heat extraction performance of the multilateral-well EGS, the effects of lateral-well geometries on multilateral-well performance should be studied and the geometrical parameters should be optimized. In this paper, we use a thermal-hydraulic-mechanical (THM) coupling model with a complex discrete fracture network (DFN) to investigate the influences of lateral-well geometrical parameters on the multilateral-well EGS performance. The lateral-well geometrical parameters include the lateral-well length, number, spacing and diameter. The results indicate that the longer lateral well and larger well spacing are beneficial for enhancing the multilateral-well EGS performance. In terms of better heat extraction performance and lower pressure impedance, the 400 m well spacing is the optimizing value under the fracture density of 0.067 m−1. The lateral-well number has a complicated effect on the heat extraction process. A large number of lateral wells can improve swept volume and reduce pressure impedance, but simultaneously connect more fractures and accelerate thermal breakthrough. Therefore, the lateral-well number should be optimized according to the specific DFN and under the DFN in this paper, 6 lateral wells are the best for the multilateral-well EGS performance. When there is a rotation angle between injection and production lateral wells, it can postpone the thermal breakthrough and be beneficial for heat extraction. The influence of the lateral-well diameter on the EGS performance can be ignored. The results of this study provide good guidance for the lateral-well design of the multilateral-well EGS.

中文翻译：

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基于热-水-机械耦合模型的侧井几何形状对多井EGS性能的影响

摘要 我们之前的研究 (Song et al., 2018) 提出了一种新型的多井增强型地热系统 (EGS) 来开发地热能，并说明多井 EGS 比传统双井 EGS 具有更好的热提取性能。然而，为了进一步提高多井EGS的排热性能，需要研究侧井几何形状对多井性能的影响，优化几何参数。在本文中，我们使用具有复杂离散裂缝网络 (DFN) 的热-水力-机械 (THM) 耦合模型来研究侧井几何参数对多边井 EGS 性能的影响。侧井几何参数包括侧井长度、数量、间距和直径。结果表明，较长的横向井和较大的井距有利于提高多井EGS性能。在更好的排热性能和更低的压力阻抗方面，400 m井距是0.067 m-1裂缝密度下的优化值。侧井数对热提取过程具有复杂的影响。大量的侧井可以提高波及体积和降低压力阻抗，但同时连接更多的裂缝并加速热突破。因此，侧井数应根据具体的 DFN 进行优化，在本文的 DFN 下，6 口侧井对多边井 EGS 性能最佳。当注采侧井有旋转角时，它可以推迟热突破，有利于热量的提取。侧井直径对 EGS 性能的影响可以忽略不计。该研究结果为多井EGS的侧井设计提供了良好的指导。