Thermal-Plume fibre Optic Tracking (T-POT) test for flow velocity measurement in groundwater boreholes

We develop an approach for measuring in-well fluid velocities using point electrical heating combined with spatially and temporally continuous temperature monitoring using Distributed Temperature Sensing (DTS). The method uses a point heater to warm a discrete volume of water. The rate of advection of this plume, once the heating is stopped, equates to the average flow velocity in the well. We conducted Thermal-Plume fibre Optic Tracking (T-POT) tests in a borehole in a fractured rock aquifer with the heater at the same depth and multiple pumping rates. Tracking of the thermal plume peak allowed the spatially varying velocity to be estimated up to 50 m downstream from the heating point, depending on the pumping rate. The T-POT technique can be used to estimate the velocity throughout long intervals provided that thermal dilution due to inflows, dispersion, or cooling by conduction do not render the thermal pulse unresolvable with DTS. A complete flow log may be obtained by deploying the heater at multiple depths, or with multiple point heaters. Raw project data is available by contacting [e-mail]本研究开发了一种结合点式电加热与分布式温度传感（Distributed Temperature Sensing, DTS）时空连续温度监测的井内流体流速测量方法。该方法通过点加热器对离散水体区域进行加热，待加热停止后，热羽流的平流速率即对应井内的平均流体流速。我们在裂隙岩石含水层的一口钻孔中开展了热羽流光纤追踪（Thermal-Plume fibre Optic Tracking, T-POT）试验，试验中加热器固定于同一深度，并设置了多种抽水速率。通过追踪热羽流峰值位置，可根据抽水速率估算加热点下游至多50米范围内的空间变化流速。只要流入引发的热稀释、弥散或传导冷却未使热脉冲无法被DTS识别，T-POT技术便可用于估算长井段内的流体流速。通过在多个深度部署加热器，或使用多点加热器，即可获取完整的流量测井数据。原始项目数据可通过联系[e-mail]获取。