Geothermal borehole on the BRGM platform (Orléans, 2021).
In order to achieve the objectives of the regional climate-air-energy plan (PCAET), the Horizon 2030-2050 plan and the Heating Network Master Plan (which aims to connect 65,000 additional homes to the existing heating networks), Orléans Métropole decided to promote the development of geothermal energy in the metropolitan area. With this in mind, BRGM was commissioned to assess the area's near-surface geothermal potential (in water tables and using probes) and deep geothermal potential (in the Dogger and Triassic aquifers) and to audit local geothermal operations that have encountered difficulties, in order to draw up a list of recommendations for the different stakeholders involved (project managers, design offices, drillers) so as to reduce the risk of failure for future operations.
In terms of near-surface geothermal energy (0 to -200 m), the work involved drawing up a map of the development potential by combining several factors: the geothermal resources, the accessibility of the resources, surface uses and needs, the technological options, the regulatory, logistical and cadastral constraints and the related costs. The map makes it possible to identify the most relevant geothermal heat-exchange technology for a given plot or district, and to estimate the degree of needs coverage according to each type of geothermal system (probes and groundwater) over the entire metropolitan area.
The work on deep geothermal energy (1,000 to 1,500m deep) involved assessing the deep subsurface resources (Dogger and Triassic) and developing a 3D geological model of the Orléans metropolitan area, thus making it possible to estimate the geothermal potential of these two types of aquifers and identify potential drilling sites, in relation to the heating-network development plan and the needs. The identification process also included recommendations based on feedback from the failure of the Triassic aquifer borehole in Melleray in the 1980s.
Finally, feedback from local near-surface geothermal projects that experienced operating difficulties highlights that the problems were either due to errors during the installation (faulty connection of surface installations, use of a defective, old piezometer) or caused by clogging when operating. The analysis of these use cases enabled us to draw up a list of recommendations to be taken into account by project managers, design offices and drillers, so as to reduce clogging risks in the future.
Using the results
The maps produced will be included in the Atlas Multi-ENR (map of multiple renewable energy sources) drawn up by Orléans Métropole (Action 7 of the 2019-2025 Action Plan) and made available to the general public.
- Orléans Métropole