Comprehensive application of hydrogeological survey and in-situ thermal response test

Abstract Thermal properties of rock-soil are of great importance for the design of borehole heat exchangers (BHEs). In the process of testing thermal properties of rock-soil through an in-situ thermal response test (TRT), groundwater seepage directly affects the evaluation of thermal properties in TRTs and leads to a varied arrangement and engineering costs of BHEs. Therefore, comprehensive hydrogeological surveys of groundwater and TRTs to determine geothermal properties are necessary. In this study, we made a preliminary attempt to use hydrogeological surveys and correlated TRTs to investigate the heat exchange efficiency of a single U-tube BHE. The geological conditions were used to predict and analyze the groundwater form, groundwater depth, and flow trajectory in the test area based on the natural electric field frequency selection method. Using a comprehensive dataset, the groundwater velocity was determined with ANSYS. The results showed that the initial temperature of rock-soil was 21.8 °C and that the comprehensive thermal conductivity of rock-soil was 1.942 W/(m·°C). Confined and phreatic aquifers existed in the test area, and the depth of the confined aquifer was approximately 70 m. The groundwater velocity in the test area was considered to be approximately 2–2.5 m/d. The results of this study confirm that TRTs combined with groundwater surveys can improve the test accuracy and consequently provide guidance for engineering practices in ground-coupled heat pump systems.