Estimating Thermophysical Parameters from In-situ Tests in Borehole Heat Exchangers

Abstract

We monitored the underground thermal recovery in a pilot geothermal plant, after modifying the equilibrium temperature-depth profile with the injection of a known heat flow for obtaining the thermal properties of the underground. The temperature-time series, recorded at 20 m depth intervals with a precise thermal logging device, were analyzed with inverse techniques based on the line-source and the cylindrical source models. The latter was approached as a best-fitting problem between the measured and computed fluid temperatures. By fitting the recorded temperature data with a least square approach, we obtained the underground thermal diffusivity and volumetric heat capacity, together with the borehole thermal resistance at several depth intervals. The results were then compared to data obtained from laboratory analysis on rock samples and from conventional thermal response tests.