Induced Temperature Gradients to Examine Groundwater Flowpaths in Open Boreholes

Abstract

Techniques for characterizing the hydraulic properties and groundwater flow processes of aquifers are essential to design hydrogeologic conceptual models. In this study, rapid time series temperature profiles within open-groundwater wells in fractured rock were measured using fiber optic distributed temperature sensing (FO-DTS). To identify zones of active groundwater flow, two continuous electrical heating cables were installed alongside a FO-DTS cable to heat the column of water within the well and to create a temperature difference between the ambient temperature of the groundwater in the aquifer and that within the well. Additional tests were performed to examine the effects of pumping on hydraulic fracture interconnectivity around the well and to identify zones of increased groundwater flow. High- and low-resolution FO-DTS cable configurations were examined to test the sensitivities of the technique and compared with downhole video footage and geophysical logging to confirm the zones of active groundwater flow. Two examples are presented to demonstrate the usefulness of this new technique for rapid characterization of fracture zones in open boreholes. The combination of the FO-DTS and heating cable has excellent scope as a rapid appraisal tool for borehole construction design and improving hydrogeologic conceptual models.

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

“…Leaf et al, 2012;Read et al, 2013Read et al, , 2014Banks et al, 2014). DTS can provide high resolution temperature data using optical fiber as the sensing medium.…”

“…Read et al (2013Read et al ( , 2014 used DTS to monitor cross-borehole thermal dilution tests and to quantify vertical flow in boreholes. Banks et al (2014) tested fiber optic cable configurations to characterize flow pathways in open boreholes. A short ($3 m long) actively heated DTS based tool that could be raised and lowered in a screened well was tested by Liu et al (2013) to characterize groundwater flux in a shallow borehole in alluvial sand and gravel.…”

Geophysical Methods for Monitoring Temperature Changes in Shallow Low Enthalpy Geothermal Systems

“…A cross well thermal tracer test was performed to identify the connection between boreholes through the fracture network. Banks et al [132] used fiber-optic DTS to measure temperature profiles in open groundwater wells in fractured rock. They used electrical heating cables to heat the water in the well and create a temperature difference with the surrounding aquifer.…”

Mapping fracture flow paths with a nanoscale zero-valent iron tracer test and a flowmeter test

“…Electrical conductivity logging can be used to detect the permeable zones in a borehole (Tsang et al 1990). Recent development of the distributed temperature sensing technology can be used to characterize the permeable fractures and hydrogeological conditions in a single borehole (Banks et al 2014;Read et al 2014;Coleman et al 2015;Bense et al 2016;Sellwood et al 2016), but the deployment of the downhole instrument may affect data acquisition (Bense Electronic supplementary material The online version of this article (doi:10.1007/s10040-017-1651-8) contains supplementary material, which is available to authorized users. Sellwood et al 2016).…”