Heat Dissipation Test With Fiber‐Optic Distributed Temperature Sensing to Estimate Groundwater Flux

Abstract

We measure groundwater flux and thermal parameters around a borehole performing a heat dissipation test by heating the armor of a single fiber‐optic cable and interpreting the resulting heating curves with a new analytical method. The procedure is similar to thermal response tests, but benefitting from the high spatial and temporal resolution of distributed temperature sensing and lasting longer, so as to measure advective dissipation. Field installation relies on an innovative method in hydrogeology, which is based on the installation of the FO cable in the annular space of the well, close to the aquifer matrix. The proposed new analytical method, expands the traditional Moving Infinitesimal Line Source Model to account for the effects of the field set up and cable materials. In fact, we show that the resulting temperature build‐up goes through four periods easy to identify using the log derivative of temperature (dT/d (ln(t))): Initial response, skin (cable insulation), conduction dominated and advection dominated. We test the proposed method in an unconsolidated shallow aquifer with controlled pumping. Results are of the same order of magnitude of independent estimates of groundwater velocity.

An ADTS Toolbox for Automatically Interpreting Active Distributed Temperature Sensing Measurements

“…However, its use is appropriate in well environment as soon as the investigated borehole is sealed using packers, flexible borehole liners (Coleman et al 2015) or temporary grout (Klepikova et al 2018). The borehole can also be permanently sealed with grout once the FO cables are installed (Selker and Selker 2018; Zhang et al 2020), but the DTS cables can also be installed behind the borehole casing, in contact with the aquifer materials (del Val et al 2021). In such cases, the use of the ADTS Toolbox could require discarding the temperature increase induced by the grout and observed before heat reaches the sediments or materials surrounding the borehole (Zhang et al 2020).…”

“…At early times, the measured temperature increase ∆ T depends on the thermal properties of the FO cable (∆ T FO ) and the heat produced is stored within the FO cable inducing a large temperature increase (del Val et al 2021; Simon et al 2021). As soon as the heat reaches the material surrounding the FO cable, conduction starts controlling heat transfers in the porous media.…”

“…ADTS methods have already been used for different applications, especially for characterizing borehole flows or groundwater fluxes in fractured media or sedimentary aquifers in various conditions, like in open boreholes (Leaf et al 2012; Liu et al 2013; Banks et al 2014; Read et al 2014; Hausner et al 2015; Read et al 2015), in sealed boreholes (Coleman et al 2015; Klepikova et al 2018; Selker and Selker 2018; Maldaner et al 2019; Munn et al 2020), or else in direct contact within sedimentary aquifers (Bakker et al 2015; Des Tombe et al 2019; del Val et al 2021). It has also been used for dam and dike monitoring to detect seepage flows (Perzlmaier et al 2004; Aufleger et al 2007; Su et al 2017; Ghafoori et al 2020) or for geothermal applications to infer the thermal conductivities distribution along boreholes (Galgaro et al 2018; Vélez Márquez et al 2018; Zhang et al 2020).…”

Estimation of Groundwater Flow Rate by an Actively Heated Fiber Optics Based Thermal Response Test in a Grouted Borehole

“…del Val et al. (2021) and Simon et al. (2021) emphasize that the “skin effect” (thermal resistance) caused by the jacket cannot be ignored when estimating the groundwater flow rate.…”

“…Since the jacket of AHFOC has low thermal conductivity, the temperature response curve of a TRT cannot be perfectly described by the MILS (Figure S1 in Supporting Information S1, presence of low thermal conductivity). del Val et al (2021) and Simon et al (2021) emphasize that the "skin effect" (thermal resistance) caused by the jacket cannot be ignored when estimating the groundwater flow rate. Different stages of thermal response were identified based on heat transfer in the jacket and porous media (subdividing two stages dominated by conduction and convection).…”