Active Distributed Temperature Sensing for high-resolution fluid-flow monitoring in boreholes

用于钻孔中高分辨率流体流量监测的主动分布式温度传感

• 批准号: NE/L012715/1
• 负责人: Victor Bense
• 金额: $ 15.67万
• 依托单位: University of East Anglia
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2014
• 资助国家: 英国
• 起止时间: 2014 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FL012715%2F1
• 关键词: Active; Distributed; Temperature; Sensing; resolution

The ability to measure the flow rates of fluids in the subsurface is critical if we are to assess and successfully manage aquifers for drinking water, geothermal energy systems, shale gas deposits, and coal gasification projects. Here, it is important to understand the interlinked relationship between fluid flows, permeabilities, and geological structure. This can be attempted through observations made in boreholes. When a borehole is installed, flow up or down the borehole may occur naturally between rock at different depths. The nearby operation of any of the above projects may disturb the fluids in the rock, disrupting the flow in the borehole. If the borehole is used to extract fluids in these engineering applications, then any variability in the flow inside the borehole indicates where the most permeable depths are. Current methods of flow measurement inside boreholes are usually made at a single location. In order to establish what is happening along the entire borehole, a probe must be repeatedly lowered, and another measurement made. This process is tedious, and when the flow is changing over time, it can be impossible to adequately determine how this is happening at all depths. On the other hand, new distributed sensors allow measurements to be made with continuous spatial coverage. Distributed Temperature Sensing (DTS) gives continuous measurements of temperature along fibre optic cables. A fibre optic cable acts as a long (100s of metres to kilometres) thermometer from which temperature measurements can be obtained up to every 12 cm. Such a cable installed in a borehole can give a highly detailed log of temperature along its entire length in just a few seconds. This is useful in itself, but exact quantification of the flows by just passively measuring the temperature is not usually possible. We believe a new method, using heated fibre optic cables and DTS, will be able to measure flow rates. With the proposed method, a cable installed centrally and running to the base of a borehole is heated uniformly by passing a current through the protective materials surrounding the optical fibre. The temperature of the cable, measured using DTS, will increase, and the increase in temperature should depend on how fast the fluid is flowing past it. Faster flows should remove heat more efficiently, lowering the cable temperature. Such a system would potentially be able to measure flows every 12 cm, and be able to detect changes occurring in the flow every few seconds.The method will be tested in a controlled way using a borehole constructed in a lab from PVC tubing. This would allow access inside and allow us to visually inspect the flow (using dyes) and equipment during testing. A prototype heated 'Active' DTS (A-DTS) system is to be installed in the tube. From a storage tank, water will be pumped through the tube at varying rates, mimicking flow inside a borehole. This will allow is to determine how the temperature of the cable changes in different flow conditions. We will then adjust the heating power of the cable, as the temperature changes due to different flows may be more readily detectable when using higher or lower powers. Finally, the temperature effect at inflow/outflow locations (as would happen where a rock is fractured) will be investigated using inflow/outflow ports in the centre of the artificial borehole. The exact set-ups and the underlying physics will be tested using advanced numerical model techniques.

如果我们要评估和成功管理饮用水、地热能系统、页岩气矿床和煤气化项目的含水层，测量地下流体流速的能力至关重要。在这里，理解流体流动、渗透率和地质结构之间的相互联系是很重要的。这可以通过在钻孔中进行观察来尝试。当安装钻孔时，在不同深度处的岩石之间可以自然地发生沿钻孔向上或向下的流动。上述任何项目的附近作业都可能扰乱岩石中的流体，破坏钻孔中的流动。如果钻孔用于在这些工程应用中提取流体，则钻孔内的流动的任何变化指示最可渗透的深度在哪里。当前的钻孔内流量测量方法通常在单个位置进行。为了确定沿整个钻孔沿着发生的情况，必须反复降低探头，并进行另一次测量。这个过程是冗长乏味的，并且当流动随时间变化时，可能不可能充分确定这在所有深度是如何发生的。另一方面，新的分布式传感器允许在连续的空间覆盖范围内进行测量。分布式温度传感（Distributed Temperature Sensing，简称感温）可对沿着光纤电缆的温度进行连续测量。光纤电缆作为一个长（100米到公里）的温度计，从它可以获得每12厘米的温度测量。这种安装在钻孔中的电缆可以在短短几秒钟内提供沿其整个长度沿着的非常详细的温度记录。这本身是有用的，但仅通过被动测量温度来精确量化流量通常是不可能的。我们相信一种新的方法，使用加热的光纤电缆和电缆，将能够测量流量。利用所提出的方法，通过使电流通过光纤周围的保护材料来均匀地加热安装在中心并延伸到钻孔底部的电缆。电缆的温度（使用温度计测量）将升高，温度的升高应取决于流体流过电缆的速度。更快的流动应更有效地带走热量，降低电缆温度。这种系统有可能每隔12厘米测量一次流量，并能每隔几秒钟检测一次流量的变化。该方法将在实验室用PVC管建造的钻孔中以受控的方式进行测试。这将允许进入内部，并允许我们在测试期间目视检查流量（使用染料）和设备。一个原型加热的“主动”冷却系统（A-冷却系统）将安装在管道中。从一个储水箱中，水将以不同的速度被泵送通过管道，模仿钻孔内的流动。这将允许确定电缆的温度如何在不同的流动条件下变化。然后，我们将调整电缆的加热功率，因为当使用更高或更低的功率时，由于不同的流量而引起的温度变化可能更容易检测到。最后，将使用人工钻孔中心的流入/流出端口，研究流入/流出位置（如岩石破裂处）的温度效应。将使用先进的数值模型技术测试确切的设置和基本的物理特性。