Fiber optic sensing has gained importance for wellbore monitoring and reservoir characterization in geothermal fields as it allows continuous, spatially highly resolved measurements. Distributed acoustic sensing (DAS) and distributed temperature sensing (DTS) technologies, among others, enable monitoring of flow regimes and heat transport inside the wellbore to describe the dynamical behavior of the reservoir. The technically challenging installation of a permanent fiber optic monitoring system in a geothermal production well over the entire wellbore length was conducted for the first time at the geothermal site Schäftlarnstraße in Munich, Germany. One cable with two DAS fibers, two DTS fibers, and one fiber for a downhole fiber optic pressure/temperature gauge were clamped to ¾-in. sucker rods and installed to 3.7 km measured depth to collect data from the wellbore after drilling, during testing, and during operations. We present DTS profiles during 3 months of well shut-in and show the results of two cold water injection tests conducted to localize inflow zones in the reservoir and to test the performance of the fiber optic setup. A vertical displacement in temperature peaks of approximately 1.5 m was observed during the injection tests, presumably resulting from thermal contraction of the sucker rod–cable setup. This was verified by analyzing the strain information from the DAS records over 1 h of warm-back after cold water injection with the calculated theoretical thermal contraction of DTS of the same period. We further verified the flowmeter measurements with a gradient velocity analysis of DTS profiles during injection. Intake to the major inflow zone was estimated to 93.5% for the first injection test, respective 94.0% for the second, intake of flowmeter was calculated to 92.0% for the same zone. Those values are confirmed by analyzing DTS profiles during the warm-back period after the well was shut.

中文翻译：

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在德国南部 Molasse 盆地的地热生产井中使用永久性光纤装置监测冷水注入以进行储层表征

光纤传感在地热领域的井眼监测和储层表征方面变得越来越重要，因为它允许连续、空间高分辨率的测量。分布式声学传感 (DAS) 和分布式温度传感 (DTS) 技术等能够监测井筒内的流态和热传输，以描述储层的动态行为。在德国慕尼黑的地热站点 Schäftlarnstraße 首次在整个井筒长度的地热生产井中安装了具有技术挑战性的永久性光纤监测系统。一根带有两根 DAS 光纤、两根 DTS 光纤和一根用于井下光纤压力/温度计的光纤被夹在 3/4 英寸处。抽油杆并安装到 3. 7 公里的测量深度，用于在钻井后、测试期间和操作期间从井眼收集数据。我们展示了关井 3 个月期间的 DTS 剖面，并展示了为定位储层中的流入区并测试光纤设置的性能而进行的两次冷水注入测试的结果。在注入测试期间观察到大约 1.5 m 的温度峰值垂直位移，可能是由抽油杆-电缆装置的热收缩引起的。这通过分析来自 DAS 记录的应变信息得到了验证，该记录在冷水注入后 1 小时内回暖，同时计算出 DTS 的理论热收缩时间。我们通过注射过程中 DTS 剖面的梯度速度分析进一步验证了流量计测量结果。对于第一次注入测试，主要流入区的进气量估计为 93.5%，第二次注入测试分别为 94.0%，对于同一区域，流量计的进气量计算为 92.0%。这些值是通过分析井关闭后回暖期间的 DTS 剖面来确认的。