Interpretation of thermal response tests in the presence of groundwater flow

A thermal response test (TRT) was conducted in a ground heat exchanger (GHE) of 50m deep drilled in a formation with groundwater flow. During the TRT, the vertical profiles of the formation temperature were monitored using an optical fiber thermometer for evaluating the vertical distribution of thermophysical properties of the formation. Between 25.0 m and 40.0 m in the GHE, measured temperature showed a slow increase during the circulation of heat medium and a fast recovery to original temperatures after the circulation, indicating the existence of an active groundwater flow in the interval. The interpretation of the TRT based on the chronological change of average temperatures of heat medium and the ground temperatures showed a marked difference in apparent thermal conductivity above and below the groundwater level. At the depth of 36.0 m and 44.3 m in an observation well close to the GHE, in-situ groundwater velocity measurements were conducted using single-borehole measurement tool to clarify the relationship between groundwater velocities and apparent thermal conductivities. The measured groundwater velocities of 0.223 m/d and 0.040 m/d, at 36.0 m and 44.3 m, respectively, showed a good agreement with the apparent thermal conductivities at each depth estimated on the basis of the vertical temperature profiles during TRT.