Heat flux evaluation based on active fiber optic distributed temperature sensing tests in southwestern Yukon, Canada

• Fibre-optic (FO) distributed temperature sensing (DTS) for geothermal evaluations. • FO-DTS thermal response test produces high-resolution thermal conductivity profile. • High-resolution allows to identify variation in substrate and flow. • Heat flux evaluation in pre-existing boreholes decreases exploration risk. • New heat flux evaluation for southwestern Yukon, Canada. Geothermal energy could decrease remote regions dependence on diesel by offering an alternative baseload energy. However, the geothermal exploration risk is high in remote regions due to limited temperature and ground thermal conductivity data, and resultant heat flux evaluations. Thermal response tests are commonly used in the heat pump industry to evaluate the effective thermal conductivity, but these tests are typically performed in shallow wells (< 200 m), assume the effective thermal conductivity to be purely due to conduction and neglect the influence of groundwater flow. Herein, fibre-optic distributed temperature sensing was used during active thermal response tests to produce a high-resolution in-situ effective thermal conductivity profile. The high-resolution profiles allow conduction-dominated segments to be isolated based on the temperature and effective thermal conductivity profiles. This method was applied to two boreholes in southwestern Yukon on the traditional territory of Kluane First Nation (KFN-L: 387 m and DRGW: 220 m). The heat flux was evaluated based on conductive segments of the temperature and thermal conductivity profiles. The temperature profile was corrected for topography and paleoclimate effects, and the internal heat generation was also considered. This resulted in heat flux estimation of 89 mW m -2 and 99 mWm -2 at KFN-L and DRGW, respectively. These values decrease exploration uncertainty around Burwash Landing, Yukon, where data scarcity is a challenge to geothermal exploration. This method could be applied in diverse geological settings to confidently estimate local terrestrial heat flux in pre-existing boreholes.