李馨馨, 李典庆, 徐轶. 地热对井系统裂隙岩体三维渗流传热耦合的等效模拟方法[J]. 工程力学, 2019, 36(7): 238-247. DOI: 10.6052/j.issn.1000-4750.2018.06.0340
引用本文: 李馨馨, 李典庆, 徐轶. 地热对井系统裂隙岩体三维渗流传热耦合的等效模拟方法[J]. 工程力学, 2019, 36(7): 238-247. DOI: 10.6052/j.issn.1000-4750.2018.06.0340
LI Xin-xin, LI Dian-qing, XU Yi. Equivalent simulation method of three-dimensional seepage and heat transfer coupling in fractured rock mass of geothermal-borehole system[J]. Engineering Mechanics, 2019, 36(7): 238-247. DOI: 10.6052/j.issn.1000-4750.2018.06.0340
Citation: LI Xin-xin, LI Dian-qing, XU Yi. Equivalent simulation method of three-dimensional seepage and heat transfer coupling in fractured rock mass of geothermal-borehole system[J]. Engineering Mechanics, 2019, 36(7): 238-247. DOI: 10.6052/j.issn.1000-4750.2018.06.0340

地热对井系统裂隙岩体三维渗流传热耦合的等效模拟方法

Equivalent simulation method of three-dimensional seepage and heat transfer coupling in fractured rock mass of geothermal-borehole system

  • 摘要: 研究地热对井系统中的裂隙岩体渗流传热问题对于开采深层地热能和发展可再生清洁能源利用技术具有重要价值。基于渗流传热耦合理论和离散裂隙网络模型,提出了裂隙岩体三维热流耦合的等效模拟方法:考虑由岩块基质及复杂离散裂隙网络组成的双重介质,采用无厚度单元模拟裂隙、线单元模拟对井,通过裂隙、对井和岩块三者之间的流量和热量交换实现渗流和传热过程耦合分析。通过与解析方法和精细模拟方法相比较,验证了等效模拟方法的有效性;并将其应用于含大规模裂隙岩体地热对井系统热采过程的数值模拟,获取了储层内温度场的分布规律,评价了裂隙开度对储层平均温度和整体开采率的影响。结果表明:该文方法能够对裂隙及井筒中的渗流传热行为进行细致模拟,在保证精度的前提下,可大幅减小计算量和计算时长;裂隙网络的非均匀及各向异性分布导致岩体温度场分布呈现高度不均匀性,反映了热流耦合的早期热突破和长尾效应等特点;裂隙内水的对流传热作用明显,冷锋面沿储层内的主要贯通裂隙网络移动,裂隙开度是影响岩体温度场分布的重要因素。

     

    Abstract: The study on the seepage and heat transfer coupling in fractured rock mass of a geothermal doublet system is of great importance to the exploitation of deep geothermal energy and clean energy utilization technology. Based on the coupling theory of fluid flow and heat transfer as well as a discrete fracture network model, the 3D equivalent numerical method is proposed to model a geothermal doublet system. Presumed that the natural fractured reservoir consists of a block matrix and discrete fracture network, the numerical simulation for thermal extraction is implemented where the zero-thickness elements and line elements are used to model complex fracture networks and inlet/outlet wells, respectively. Seepage flow and heat transfer in fractures, wells and matrix are calculated, along with their flux and heat exchange. The proposed method is validated against results from the analytical models and refined modeling approach, and further employed for modeling the thermal recovery process in fractured rock mass containing large-scale fracture network and for assessing the effects of fracture apertures on average temperature and heat extraction ratio. It shows that the proposed method is capable to precisely simulate the hydraulic-thermal behaviors in discrete fractures and wells, which would bring down the computational cost on the premise of ensuring calculation accuracy. The temperature field in fractured rock mass is nonuniformly distributed due to the spatial inhomogeneity and anisotropy of fracture network. And the characteristics of flow and heat transfer could also be captured. The cold front moves along the percolated fracture network, and the convective heat transfer of fluid is obviously observed. Fracture aperture is an essential factor affecting the heat transfer.

     

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