Flow and heat transfer numerical modelling in the Hainaut limestone geothermal reservoir: study at local and regional scales

Nowadays, Europe needs to produce more sustainable energy. A possible solution includes geothermal energy. Many sites are already in activity for example in France, Germany or Italy. In Belgium, research is currently performed in the Campine Basin. In the Mons area (South-West Belgium), some wells have been exploited since the eighties. They were drilled in a deep limestone r eservoir characterized by some highly permeable breccia levels. This reservoir has not been studied extensively, despite potentially important heat reserves. In this context, the MOREGEO project has been initiated by the University of Mons and the IDEA (intercommunity active in the area) with financial support from the ERDF European program. The general objective of this project is to drill a new geothermal doublet to provide heat to the largest city hospital. Hot water will be pumped from a well and cold water will be reinjected in another one. Specific objectives of the project include: (1) Modelling heat transfers at the scale of the new geothermal doublet; and (2) Modelling the whole geothermal reservoir in order to provide an efficient management tool for the future development of additional geothermal wells. The geothermal reservoir of Hainaut is mainly composed of limestone from the Carboniferous period, with breccia and evaporites levels. Three wells currently provide energy for the heat production to two hospitals, schools, station, housings and economic areas. The depth of the exploited layers is around 2000 meters and the pumping groundwater temperature is about 70℃. A numerical model has been developed at the scale of the future new geothermal doublet with and without heterogeneity. Numerical models are implemented using Hydrogeosphere. This calculation code simulates fluid flow, solute and heat transport in porous and fractured media. The model aims at analysing the conditions of the exploitation, the longevity of the system, and the possible interactions with surrounding geothermal wells. The reservoir includes layers of anhydrites, partly or totally dissolved according to the location. Simulations show that the parameters expected in the area allow the exploitation of geothermal wells to provide hot water for heating. Cold water injected at the reinjection well goes in the direction of the pumping well, located 1,400 m away. The longevity of the exploitation depends on the time taken by cold water to induce a decrease of temperature at the pumping well. A sensitivity analysis of the model parameters has also been carried out to see which parameters have the most important impact on the exploitation and the longevity of the geothermal doublet system. The results show the influence of the permeability of the exploited rock layer. The thickness of the layer and the flow rate in the pumping and reinjected wells have also to be considered as important parameters.