| Abstract |
The geothermal reservoir of Hainaut is a mainly carbonated fissured and karstic aquifer, composed by Lower Carboniferous limestone and dolostone. It is located in the Mons region (see Figure 1), near the French border. This geothermal resource was first discovered in 1976 thanks to a geological exploration borehole in Saint encountered massive layers of anhydrite in the Upper and Middle Visean carbonate, overlying a thick productive layer of breccias at 2.500 m deep. This borehole, that was turned into a production well ten years later, is the starting point of a district heating system. It gives 73°C hot water at an artesian flow rate of 100 m³/h. Two other wells were drilled short after the Saint Douvrain and Ghlin, a few kilometers North and North first one is exploited for heating buildings and sanitary water of a nearby hospital. The second one is still inactive. These two wells produce respectively 67°C and 71°C water, at 1.370 m and 1.575 m deep, from Upper Visean breccia. The flow is artesian as well as in Saint-Ghislain, and reaches the same value (100 m³/h). Another geothermal well drilled in 1985 in Condé (France), a few kilometers off the border, produced water This heterogeneous temperature distribution demonstrates the reservoir before any new exploitation prospect. Presently, the exploitation scheme of the reservoir is extremely simple. The two exploited wells draw water from the depths, use heat in a serie of heating applications, and then discharge cooled water to the hydrographic networks, thanks to its low salinity (less than 2g/l). Recent development programs involve present networks extension and new drilling works. Further investigations have to be led in the aim of avoiding other failure as it occurred in Condé and predicting the limitations of the single-well technique, amongst others. The reservoir is thought to be recharged from infiltrat in the outcropping area. It has no natural exsurgence, except showing anomalies in temperature and/or chemical content. In the aim of assessing the influence of deep water on shallow water characteristics an extensive study has been made to gather chemical and isotopic data deep and shallow waters of this aquifer. |