Groundwater flow characterization in a fractured bedrock aquifer using active DTS tests in sealed boreholes

In recent years, wireline temperature profiling methods have evolved to offer new insight into fractured rock hydrogeology. Important advances in wireline temperature logging in boreholes make use of active line source heating alone and then in combination with temporary borehole sealing with flexible impervious fabric liners to eliminate the effects of borehole cross-connection and recreate natural flow conditions. Here, a characterization technique was developed based on combining fiber optic distributed temperature sensing (DTS) with active heating within boreholes sealed with flexible borehole liners. DTS systems provide a temperature profiling method that offers significantly enhanced temporal resolution when compared with conventional wireline trolling-based techniques that obtain a temperature–depth profile every few hours. The ability to rapidly and continuously collect temperature profiles can better our understanding of transient processes, allowing for improved identification of hydraulically active fractures and determination of relative rates of groundwater flow. The advantage of a sealed borehole environment for DTS-based investigations is demonstrated through a comparison of DTS data from open and lined conditions for the same borehole. Evidence for many depth-discrete active groundwater flow features under natural gradient conditions using active DTS heat pulse testing is presented along with high resolution geologic and geophysical logging and hydraulic datasets. Implications for field implementation are discussed.

Raw project data is available by contacting [e-mail]

近年来，电缆式温度剖面测井（wireline temperature profiling）方法不断演进，为裂隙岩石水文地质研究提供了全新的认知视角。井眼电缆温度测井领域的重要进展，先后采用仅依托有源线源加热的方案，随后结合柔性防渗织物衬垫开展临时井眼密封，以消除井眼串流效应并复现自然流场条件。本研究开发了一种表征技术，将光纤分布式温度传感（fiber optic distributed temperature sensing，DTS）与经柔性井眼衬垫密封的井眼内有源加热技术相结合。相较于传统需每隔数小时获取一次温度-深度剖面的电缆拖拽式测量技术，DTS系统具备显著提升的时间分辨率温度剖面测量能力。快速连续采集温度剖面的能力，能够深化对瞬态过程的认知，助力更精准地识别水力活跃裂隙，并确定地下水流的相对速率。通过对同一井眼在裸眼与衬管条件下的DTS数据进行对比，验证了密封井眼环境在基于DTS的水文地质调查中的优势。本文结合高分辨率地质、地球物理测井与水文地质数据集，展示了利用有源DTS热脉冲测试在自然梯度条件下识别出的多处深度离散型活跃地下水流特征，并讨论了该技术的野外实施启示。原始项目数据可通过联系[e-mail]获取。