Heat Energy storage through semi-opened circulation into low permeablility hardrock aquifers – Stock-en-Socle

The Stock-en-socle project aims at acquiring the necessary knowledge for the periodic storage of sensitive heat in hardrock aquifers characterized by their low permeability. Though geothermal energy storage boreholes remain the only existing solutions proposed in a low-permeability environment, Stock-en-socle examines the possibilities of heat storage through semi-open circulation of water in a well. This is, typically, a SCW (Standing Column Well) and takes advantage of the strong heterogeneity of hardrock aquifers, targeting zones that are the least favorable for water-resource exploitation. The main identified scientific problems facing the project concern the minimum level of permeability required around the well and its evolution with time (increase and decrease) through water-rock interaction processes. A scientific and technical program, including modeling and experimental laboratory and fieldwork, will study the thermal, hydraulic and geochemical processes involved. The study area for field tests, located in French Brittany, will test different geological settings (granite, gneiss and schist). Tracer tests and a long-term circulation test by injection of warm water within a single well (push-pull), will be carried out. Hydrothermal modeling will study the effects of permeability structures on the capacity of storage and recovery of thermal energy, while reactive-transfer modeling will simulate the evolution of permeability under the impact of dissolution and precipitation reactions. Based on the obtained results, technical solutions will be studied for drilling and equipping an SCW well in a low-permeability context. This work will be completed by a technical/economic feasibility study for proposing an investment and operations model. The end result will be description of the suitability of heat storage in SCW well connected to a small heat-distribution network. To reach the defined goals, Stock-en-Socle will be based on a public/private partnership with two public institutions devoted to research activities, a university and a public establishment with an industrial and commercial character, and two private companies working in the field of geothermal energy and soil technology. In addition to the dissemination of its results to the scientific community, Stock-en-socle will identify the possibilities for further work as part of the project, in terms of setting up an industrial research project to be implemented in Brittany.