A workflow for bedrock thermal conductivity map to help designing geothermal heat pump systems in the St. Lawrence Lowlands, Québec, Canada

An accurate knowledge of the subsurface thermal conductivity is essential to design geothermal heating and cooling systems, specifically ground-coupled heat pumps. The subsurface thermal conductivity has a direct impact on the length of vertical ground heat exchangers needed to fulfill building energy needs. However, mapping the distribution of the subsurface thermal conductivity is a significant challenge due to the ground heterogeneity and the limited radius of influence associated with thermal conductivity assessment methods. Data from 79 thermal response tests, 90 thermal conductivity analyses conducted in the laboratory, and geophysical well logs from 72 oil and gas exploration wells were combined and analyzed together in an attempt to map the bedrock thermal conductivity distribution of the St. Lawrence Lowlands, Quebec, Canada. Results from laboratory and well log analysis were adjusted for field scale-effects using thermal response tests to properly define a statistically reliable thermal conductivity for each thermostratigraphic unit of this sedimentary basin. The thermal conductivity obtained from thermal response tests and adjusted laboratory analyses was interpolated with sequential Gaussian simulations to generate a two-dimensional bedrock thermal conductivity map, which can be used by geothermal system designers to better understand the geothermal heat pump potential of the St. Lawrence Lowlands.