Heterogeneous bedrock investigation for a closed-loop geothermal system: A case study

Abstract

a b s t r a c tThis paper investigates bedrock heterogeneity by applying three different geophysical approaches, in order to study the long-term behaviour and the interaction between closed-loop geothermal systems. The investigated site consists of four boreholes equipped with geothermal pipes on the campus of University of Liege, Belgium. The first approach includes acoustic borehole imaging, gamma-ray logging and cuttings observation and results to a detailed fracture characterisation, rock identification and layer dip angle determination. The second approach consists of measuring the thermal conductivity of cuttings at the laboratory. Study of cuttings thermal conductivity measurements can contribute to bedrock heterogeneity knowledge concerning the transition of one formation to another and the layer dipping. The third approach is based on high-resolution temperature profiles, measured during the hardening of the grouting material and the recovery phase of a Distributed Thermal Response Test. Through this approach a correlation of the temperature profiles to the geological characteristics of the surrounding bedrock is identified. The analysis of this correlation can provide information on fractured zones, alternation of different rock types and layering dipping. This latter approach can be easily applied on closed-loop geothermal systems to characterise the bedrock and investigate its heterogeneity as well as contribute to the their long-term behaviour prediction and to the optimisation of their efficiency.

Experimental and numerical investigation of a long-duration Thermal Response Test: Borehole Heat Exchanger behaviour and thermal plume in the heterogeneous rock mass

“…The ending time point was chosen at 60 h (typical TRT duration). The calculated thermal conductivity by this approach is equal to 2.90 W/mK and is in good agreement with the corresponding values of TRTs in the other three BHEs (difference less than 0.1 W/mK; Radioti et al, 2016). The volumetric heat capacity was taken equal to 2300 kJ/m 3 K, based on literature values for the in-situ rock types (Smolarczyk, 2003;Nguyen and Lanini, 2012).…”

“…The bedrock consists mainly of siltstone and shale interbedded with sandstone layers and the average layer dip angle is approximately 45°SE. A detailed bedrock characterisation based on borehole televiewer measurements, laboratory measurements and temperature profiles analysis is presented in Radioti et al (2016).…”

Colloquium 2016: Assessment of subsurface thermal conductivity for geothermal applications

“…The methods can help to characterize the subsurface with downhole acoustic and gamma ray logs to identify fractures and lithology (Radioti et al 2016). Surface resistivity surveys have also been used to image the temperature perturbation of operating geothermal systems (Arato et al 2015;Giordano et al 2016).…”

Effect of undisturbed ground temperature on the design of closed-loop geothermal systems: A case study in a semi-urban environment

“…The cables were tapped every 50 cm at the outer surface of the pipes. Additionally to the fiber optic cables and in direct contact [36]. The mean ground thermal conductivity is 2.88±0.16 W/mK, based on TRTs conducted in situ in the four BHEs [37].…”