| Abstract |
The Triassic sandstone aquifer offers on a regional scale, a large potential for lowtemperature geothermal exploitation in the Paris Basin. The Na-C1 water in the aquifer has highly variable mineralization (TDS = 4 to 110 g / l ) and a wide range of temperature (50? to>lOO?C). Chemical studies have been carried out on the Melleray site near OrlBans, where a single well was producing a Na-C1 geothermal water (TDS = 35 g / l ) at a wellhead temperature of 72?C to provide heat for greenhouses. The purpose of these studies is to understand the chemical phenomena occurring in the geothermal loop and to determine the treatment of the fluid and the exploitation procedures necessary for proper reinjection conditions to be achieved. During the tests performed after the drilling operations, chemical variations in the fluid were noticed between several producing zones in the aquifer. Daily geochemical monitoring of the fluid was carried out during two periods of differing exploit at i o n conditions, respectively pum ing Vertical heterogeneities of the aquifer can explain the variation s observed for the high flowrate. F i l t ration experiments revealed that the particle load varies with the discharge rate and that over 95 weight % of the particles are smaller than 1 pm. The chemistry of the p articles varies greatly, according to their origin as corrosion products from the well casing, p article s drawn out of the rock or minerals newly formed through water-rock reactions. at 148 m3/h and artesian flow at 36 m 5 /h. Finally, small-scale oxidation experiments were carried out on the geothermal fluid to observe the behaviour of Fe and S i O z and to favour part i c l e aggregates for easier filtration or decantation processes. |