Abstract A clear understanding of the convective heat transfer characteristics in the three-dimensional (3D) rough rock fracture is important for evaluating heat recovery in fractured reservoirs. A granite sample containing a Brazilian-induced artificial fracture, which was tested at increasing normal compressive stresses, was adopted to build 3D numerical models for rough rock fractures. At each stress level, flow-through simulation tests with different injection velocities were performed to examine the effect of fracture geometrical alterations induced by changing stresses on the heat transfer processes within hot fractured rock samples. Meanwhile, a hypothetical rough fracture and a parallel plate fracture, with an equivalent mechanical aperture to the artificial fracture, were constructed for the same heat transfer simulations as references. The results show that the flow and heat transfer behaviors in three types of fractures are significantly different, and the difference becomes more obvious as the normal stress and flow velocity increase. The alterations in asperity contacts and void spaces due to stress changes increase the heterogeneities of the distributions of streamlines and water temperatures in the artificial fracture. The tortuosity induced by the global fluctuation of the surface roughness in the hypothetical fracture cannot describe the flow and heat transport in the artificial fracture. The heat transfer coefficient in three types of fractures decreases non-linearly as the hydraulic aperture increases. Under the same hydraulic aperture, the heat transfer coefficient is larger in the hypothetical fracture than in the other two fractures. The channeling flow within the artificial fracture under high normal stresses weakens the heat transfer, resulting in the smallest heat transfer coefficient compared to the other two fractures. An empirical model was developed to describe the relationship between the normalized heat transfer coefficient and the hydraulic aperture, and this model was validated well using the published heated flow-through experimental results.

中文翻译：

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具有异质孔径的 3D 粗糙岩石裂缝中的传热

摘要 清楚地了解三维 (3D) 粗糙岩石裂缝中的对流传热特性对于评估裂缝性储层的热回收非​​常重要。采用包含巴西人工裂缝的花岗岩样品，在增加的法向压应力下进行测试，用于构建粗糙岩石裂缝的 3D 数值模型。在每个应力水平上，进行了不同注入速度的流通模拟测试，以检查由变化的应力引起的裂缝几何变化对热裂隙岩石样品内传热过程的影响。同时，假设的粗糙断裂和平行板断裂，其机械孔径与人工断裂等效，用于相同的传热模拟作为参考。结果表明，三种裂缝中的流动和传热行为存在显着差异，并且随着法向应力和流速的增加，差异变得更加明显。由于应力变化引起的凹凸接触和空隙空间的变化增加了人工裂缝中流线和水温分布的不均匀性。假设裂缝中表面粗糙度的全局波动引起的曲折不能描述人工裂缝中的流动和传热。随着水力孔径的增加，三种裂缝中的传热系数呈非线性降低。在相同的水力孔径下，假设裂缝中的传热系数大于其他两个裂缝。高法向应力下人工裂缝内的窜流削弱了传热，导致与其他两个裂缝相比传热系数最小。开发了一个经验模型来描述归一化传热系数与水力孔径之间的关系，并且使用已发布的加热流通实验结果很好地验证了该模型。