Mapping temperatures of complex shallow geothermal resources under Bordeaux urban area, using external-drift kriging.

Summary The adequate design of heat and cold supply from open-loop shallow geothermal systems requires a reliable knowledge of expected aquifer temperatures from the early stages of any building project. In order to assist Bordeaux Metropole in reaching ambitious renewable energy targets, a new approach has been proposed for mapping temperatures of shallow geothermal resources over the urban area. First a 21-layers 3D geological model has been built from geological logs to describe the geometry of geological layers and main aquifers, which allowed integrating structural data at detailed scale. Furthermore thermal logs from water wells were interpreted to characterize the mean geothermal gradient of the area, and to provide discrete aquifer downhole temperatures. Then interpolation of groundwater temperatures has been completed over the main aquifers, taking into account the geometries of layers with external-drift kriging. This enabled the production of maps at an appropriate scale (100 x 100 m mesh) for operational purposes, with improved reliability in this area affected by a complex fault network. This reliability highly depends on the density of measurement points, which appears to be adequate in key areas for urban planning.