Évaluation expérimentale de l'impact de l'opération d'un puits à colonne permanente sur les risques de précipitation minérale dans un aquifère carbonaté

Urbanization and densification concentrate more and more important needs for heating and climatization, asking for more and more efficient and compact solutions. The standing column well is a very low geothermal system particularly interesting in that case and more generally in low permeability aquifers. Little work has been done on the geochemical impacts such a system could have on groundwater, especially in carbonated aquifers and the related hazards of scaling and clogging. A numerical model and laboratory experiments have been realized but no experimental in-situ study has been carried about carbonated precipitation hazards in a regional context. This project aims to experimentally assess the geochemical impact of the operation of a standing column well in a carbonated aquifer. In order to better understand water circulations between the main well and the injection well, in particular during a bleed, tracer tests are conducted. They highlight a quick and near surface hydraulic communication and the extent of the renewal by ambient hydrogeological circulations. To determine the role of the regional underground hydrochemistry in the water quality observed in the main well and its evolutions, physical-chemical, chemical and isotopic parameters are monitored and put into perspective with larger scale data. Calcium concentrations are mainly controlled by groundwater intakes and there is a triple origin of salinity. This monitoring also informs about the impact of the operation of the geothermal unit on the chemistry of the main well, particularly on the precipitation and dissolution of calcite. The latter is very limited, the chemistry of carbonates is above all controlled by regional groundwater intakes and equilibrium reactions between dissolved CO2, bicarbonates and carbonates.