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Electrical conductivity versus temperature in freezing conditions: a field experiment using a basket geothermal heat exchanger

Citation

Revil, Andre; Coperey, A.; Stutz, B. (2019), Electrical conductivity versus temperature in freezing conditions: a field experiment using a basket geothermal heat exchanger, Dryad, Dataset, https://doi.org/10.5061/dryad.0p2ngf1w2

Abstract

In-situ experiment. Geothermal setup: Five heat exchangers (HE) are arranged in a line and are buried between 1.1 and 3.5 meters. Just two baskets worked: one (HE.5) for a correct functioning of the heat pump and the other (HE1) to freeze the ground. only, this last exchanger (HE1) has been monitored in temperature and electrical resistivity tomography. The basket HE.5 is too far away to have an influence during this experiment, the heat pump was started at 0 hour and worked during 518 hours. The temperature of ground was recorded every minutes, thanks to 41 probes (4 wire Pt100), divided into 7 vertical profils. theses profiles are located at 0, 3, 6, 7, 8, 11, 20, 21 meters (x-distance), and the used heat exchangers are at 7 meters for the HE.1 and at 24 meters for the HE.5, respectively. Electrical Resitivity Tomography (ERT): Before and during the running of the geothermal system, gephysical monitoring was carried out. At the end, nine tomography images were recorded using a SAS-1000 Terrameter (ABEM) associated with 64 electrodes arranged in straigth line (2D acquisition, with a spacing between electrodes of one meter). Apparent resisitivities were inverted with IP4DI software, incorporating spatial and time regularization --Laboratory experiments-- we sampled the soil around the exchanger using an auger. the soil consists of a mixture of clay, silts and some gravels. Two samples are selected in order to conduct some electrical measurement at different temperature. They were dried and then saturated with water from the aquifer (0.117 S/m at 27°C) and put in a thermo-regulated bath (KISS K6 from Huber). At each temperature level, a SIP spectrum was performed with ZSIP, from 0.01 hz to 45 khz.Temperature levels are  20, 15, 10, 5, 2, 0, -2, -4, -6, -8, -10, -14, -18°C. FIles--- Field. Temperature measurements and inverted resitivity: This file contains the temperature measurements and inverted resistivities from geophysical monitoring, presented in the article.  Field. Comparaison conductivity vs temperature: This file corresponds to the data extracted from the temperature and inverted resistivity sections in order to attest the resistivity vs temperature relationship.  - Laboratory. Comparaison conductivity vs temperature: This file contains the data of the phase and quadrature conductivity as a function of temperature for both samples measured in the laboratory by SIP method.