When water is injected into a fracture-dominated reservoir that is cooler or hotter than the injected water, the reservoir permeability is expected to be altered by the injection-induced thermo-mechanical effects, resulting in the redistribution of fluid flow in the reservoir. These effects are important to be taken into account when evaluating the performance and lifetime particularly of Enhanced Geothermal Systems (EGS). In this paper, we compare the results from two dye tracer tests, conducted before (at ambient temperature of $$13\,^{\circ } \text {C}$$) and during the injection of $$45\,^{\circ } \text {C}$$ hot water into a fractured crystalline rock at the Grimsel Test Site in Switzerland. Conducting a moment analysis on the recovered tracer residence time distribution (RTD) curves, we observe, after hot water injection, a significant decrease in the total tracer recovery. This recovery decrease strongly suggests that fluid flow was redistributed in the studied rock volume and that the majority of the injected water was lost to the far-field. Furthermore, using temperature measurements, obtained from the same locations as the tracer RTD curves, we conceptualize an approach to estimate the fracture surface area contributing to the heat exchange between the host rock and the circulating fluid. Our moment analysis and simplified estimation of fracture surface area provide insights into the hydraulic properties of the hydraulically active fracture system and the changes in fluid flow. Such insights are important to assess the heat exchange performance of a geothermal formation during fluid circulation and to estimate the lifetime of the geothermal formation, particularly in EGS.

中文翻译：

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溶质示踪剂测试定量分析了在水力激发的晶体中注入热水的影响

当将水注入比注入水冷或热的裂缝占主导地位的储层中时，储层的渗透率预计会因注入引起的热机械作用而改变，从而导致储层中流体的重新分布。在评估性能和使用寿命时，尤其是增强型地热系统（EGS）的性能和使用寿命时，必须考虑到这些影响。在本文中，我们比较了两种染料示踪剂测试的结果，分别在之前（在环境温度为$$ 13 \，^ {\ circ} \ text {C} $$）和注入$ 45 \，^ {\期间进行circ} \ text {C} $$热水注入瑞士格里姆瑟尔试验场的一块破裂的晶体岩石中。对回收的示踪剂停留时间分布（RTD）曲线进行力矩分析，我们观察到注入热水后，示踪剂总回收率显着下降。采收率的下降强烈表明，流体流重新分布在所研究的岩体中，并且注入的水大部分流失到了远场。此外，使用从示踪剂RTD曲线从相同位置获得的温度测量值，我们概念化了一种方法，用于估算有助于基质岩石与循环流体之间进行热交换的裂缝表面积。我们的矩分析和简化的裂缝表面积估算提供了对液压主动裂缝系统的水力特性和流体流量变化的见解。这些见解对于评估流体循环过程中地热层的热交换性能以及评估地热层的寿命非常重要，