Thermal response testing of a fractured hard rock aquifer with and without induced groundwater flow

This study quantifies experimentally the influence of groundwater on the thermal conductivity measurements via thermal response tests (TRT) in a fractured hard rock with low matrix permeability. An artificial groundwater flow towards a nearby well was induced by groundwater extraction and a TRT performed simultaneously. The results were compared with a TRT performed 24 days later in the same well without groundwater extraction. The effect of the groundwater flow is shown indirectly by the enhanced effective thermal conductivity and directly through the comparison of temperature profiles before and 4 h after both TRTs. Simulations in FEFLOW show that a groundwater flow velocity of 130–1,300 m d−1 through one open horizontal fracture of small volume increases the effective thermal conductivity by 11 % in the studied system.