| Abstract |
Experiences from the O&G and geothermal energy industry indicated, that reinjection of the cooled geothermal water into a sandstone aquifer often leads to a reduction of the permeability of the formation and the exploitation at a reduced flow rate. The reinjection pressure has to be increased in order to maintain the injection rate and the economics become very poor. The phenomenon can be attributed to various reasons: microbiological effects, water sensitivity of sandstones, suspended solids, fine migration in the reservoir, trapped gases, air contamination? Numerous geothermal doublets in Europe faced this type of problems and consequently have been abandoned in France, Hungary, Germany and Romania. Nevertheless, one of the last doublet drilled in the Netherlands, to heat greenhouses, have proved also that sandy geothermal reservoir have a great future. Two recent operations in the Paris area have proved that in non-saline environment this type of geothermal doublet should be a success using simple methods. The first plant is built in Issy-Les-Moulineaux (2012-2013) address to the geothermal reservoir of the Albian sands, it is still in commissioning phase and the second is tapping the fine grained and argillaceous detrital formation dated Neocomian. The cretaceous formations are well known since 1850, the date of the first deep well drilled in Paris. A first attempt in Front de Seine had demonstrated 20 years ago that the doublet concept is possible in detrital formations with high permeability (1 to 5.10- 3 m2/s) but only with a reduced injection flow rate. The new doublets have been designed in order to be capable to produce 200 m3/h at a minimum of 30°C with injection at 10°C giving a geothermal installed power of 4, 7MWth.The second geothermal doublet has been installed in Le Plessis-Robinson (2012-2013) and operated since nearly one year, 5 kilometres away, but in this case the geothermal reservoir was unknown, the permeability prognosis is lower compared to Albian sands in correlation with the extreme fine grained sands which were expected and equipped. The two doublets have good results because of large drilling diameters, pre-gravel packed screens, long stimulation with air lift with the highest testing flow-rate and high grade filtration in order to avoid particles in the injection well. The two plants use heat pumps decentralized for Issy and centralized in Le Plessis Robinson in order to supply DH, each corresponding to annual energy saved of about 50 GWth for heating purpose and sanitary hot water. Several other projects are ongoing in the north of Paris (Batignolles) and many others in the western part of the zone where the Dogger is unproductive (Plateau deSaclay, Versailles ect?) |