Hydraulic characterization of aquifers by thermal response testing: Validation by large-scale tank and field experiments

Abstract

[1] Thermal response tests (TRTs) are a common field method in shallow geothermics to estimate thermal properties of the ground. During the test, a constantly heated fluid is circulated in closed tubes within a vertical borehole heat exchanger (BHE). The observed temperature development of the fluid is characteristic for the thermal properties of the ground and the BHE. We show that, when the BHE is installed in an aquifer with significant horizontal groundwater flow, this test can also be used for hydrogeological characterization of the penetrated subsurface. An evaluation method based on the moving line source equation and considering the natural occurring variability of the thermal transport parameters is presented. It is validated by application to a well-controlled, large-scale tank experiment with 9 m length, 6 m width, and 4.5 m depth, and by data interpretation from a field-scale test. The tank experiment imitates an advection-influenced TRT in a well-known layered aquifer. The field experiment was recorded with a 100 m deep BHE, installed in a gravel aquifer in southwest Germany. The evaluations of both experiments result in similar hydraulic conductivity ranges as determined by standard hydraulic investigation methods such as pumping tests and sieve analyses. Thus, advection-influenced TRTs could also potentially be used to determine integral hydraulic conductivity of the subsurface.

On the applicability of the moving line source theory to thermal response test under groundwater flow: considerations from real case studies

“…Therefore, the considerations on the applicability of the MLS analysis to the case studies analyzed in this paper cannot be based on the capability of such model to estimate ground and groundwater properties correctly. Indeed performing quantitative hydro-geological investigations in situ like pumping tests (Wagner et al 2014) is an expensive procedure, often requiring the drilling of more than one test borehole. The average ground thermal conductivity in situ can in principle be derived from laboratory measurements of homogeneous portions of the core sample extracted.…”

“…In a subsequent study, Wagner et al (2014) apply the MLS model to interpret both large-scale tank and field TRT experiments. They demonstrate that the test can also be used for hydro-geological characterization of the subsoil, since in both cases the evaluations of both experiments resulted in similar hydraulic conductivity ranges as determined by standard hydraulic investigation methods such as pumping tests and sieve analysis.…”

A review on thermal response test of ground-coupled heat pump systems

“…The presented analytical approach revealed that there was a systematical misfit between actual and estimated Darcy velocities and expanded the field of application of the TRT to advection-influenced conditions beyond a Darcy velocity of 0.1 m day À 1 . Furthermore, Wagner et al [58] proposed an advection sensitive TRT evaluation as a potential method to estimate Darcy velocity and integral aquifer hydraulic conductivity. For demonstrating the applicability, the correction term-based TRT evaluation [57] is integrated in a two-step fitting approach.…”

Taylor dispersion in a packed pipe with wall reaction: Based on the method of Gill’s series solution

“…For instance, groundwater flow in soils [12], chemical separation or purification of mixtures [13,14], extraction of energy from geothermal regions [15], and contaminant transport in wetlands [16][17][18][19][20][21][22][23], which cannot be described by the model of dispersion in a pure fluid flow. The model of dispersion in porous media with wall reaction is therefore highly in need.…”