Objetivo Performance and exploitation of a geothermal doublet in the fragmented aquifer of the Madrid Basin, for the supply of central heating and sanitary hot water to teaching, hospital, social, and National Trust buildings of the Region of Madrid, situated on the Colmenar road between Kms 13 and 15 North of Madrid, and for the operation of greenhouses.On being a fragmented aquifer where there are alternating layers of sandstone and clay, it would be and absolute innovation in the European Community, with the possibility of applying the techniques developed in the operation to other possible operations in other European countries.In the case of Madrid, it is also innovative regarding the establishment of a heating distribution network for supply of central heating and sanitary hot water and "waterfall" utilization (greenhouse).In short, we can safely say that the first well has accomplished the desired goal on drilling into a geothermal resource between 1500 and 2000 metres consisting of sands and sandstones containing water at 75-76 deg. C.Tests carried out suggest the store's transmissiveness to be in the vicinity of 45 Darcy m, which means an excellent geothermal reservoir with a useful thickness of approximately 100 metres.The water contains no H2S and the gas/water ratio is 2% of volume, that is, 20 ml of gas per litre of water.The CO2 content in this gas, as established by field findings, is 2.5% of volume. Bubble-point is approximately 1 atmosphere.Average salinity in the field is approximately 20.25 gm/litre.Finally we suggest performing the second well (deviated) to a depth of 2150-2000 m., because the reservoir, according to findings of the first well, continues on below 2000 m., and in this manner a temperature nearer 80 deg. C could be reached.The high permeability areas are less sensitive to injection of particle suspensions than the low permeability areas. In view of the neutron logging, it is envisaged that the particles of the more sandy parts of the sounding (not studied in the bore samples) will be even less sensitive to such particles.It seems clear that the best solution when putting the doublet into operation would be to take the utmost care to ensure that the more permeable layer remain undamaged, disregarding from the outset the low permeability layers. The filtering system needed to avoid damage to the latter layers could tender the project pure economical.The studies carried out reveal that in order to have any chance of success in avoiding clogging, it will be necessary to filter down the particle size of a least down to 2 to 3 microns.With a view to avoid excessively large filters, we suggest tha before passing through the filters, the brine should circulate through a decanting tank.In this respect it is worth noting that the settling rate of13 micron particles is in the vicinity of 50 cm./hour. The decanter should be designed to eliminate the majority of particles larger than 13 microns.It seems likely that during operation of the geothermal doublet it will be necessary to regularly sour the well in order to repair the damage that, despite all filtering precautions, may arise. In this respect it would seem advisable to carry out souring studies of the clays by means of bore sampling taken from future wells in order to ascertain the most fitting composition of the solutions to be employed.In fact, even after maximum filtering of the particles, other particles or aggregates may form during injection, which will damage the formation.Throughout the surface circuit, which includes pumps, filters, exchangers, decanters, etc., all air content must be suppressed completely in order to prevent formation of iron hydroxides and greater flocculation of clays. The presence of oxygen could, moreover, corrode the tubes in the injection well.The exploration well drilled in the first stage has encountered a sizeble geothermal aquifer from 1600 to 2000 metres consisting of sands, sandstones, and tertiary clays, and which contains water at a temperature of 75-76 deg. C. Initial tests reveal transmissivity of some 45 Darcy m, which means an excellent aquifer with a useful thickness of 100 metres.In view of these results and since the geothermal reservoir continued at 2000 metres, we suggest drilling the second well down to 2150-2200 metres, thus reaching a temperature of 80 deg. C. This well must be deviated in such manner that at reservoir level, the separation between the injection well and the production well be 900-1000 metres, according to the calculations performed for the cold front transmission model.Regarding the diameters, the drilling program for the deviated well will be similar to that of the vertical one. Deviation will commence at 450 metres, from where it will proceed in a straight line to the reservoir.The required deviation is 43-45 deg. C, and overall well length will be about 2400 metres. After drilling is finished, production test will be carried out to determine the characteristics of the geothermal resource. The most important of these tests is a complete and prolonged test of the geothermal "doublet", simulating normal exploitation conditions with geothermal fluid cooling, and its passage through the filtering and chemical treatment installations. For this test it is essential to duplicate the sealing conditions in the circuit that will have to be maintained during exploitation. There will be a special study of the pressure variations in the injection drilling, both with the injected flowrate and with injection time.When constructed the results of the loop production injection tests are known the surface installations will be constructed.Such installations are divided in three circuits.The primary circuit is the geothermal circuit and it include the extraction and injection pumps, the filtering and chemical treatment station, the titanium exchanger and the connection pipes in glass fibre.The secondary circuit has the distribution lines (outlet and return) with variable diameters according to line and circulation pumps.The tertiary circuits are in the central heating and hot water system of each user. In these circuits, a distinction must be made between those for heating and for hot tap water.The former include the steel plate heat exchangers, the circulation pumps, heat counter and the three-way valve. The latter include the heat exchanger, circulation pumps, filter, volumetric meters, three way valves and accumulators. Programa(s) ENG-THERMIE 1 - Programme (EEC) for the promotion of energy technology in Europe (THERMIE), 1990-1994 Tema(s) 3.2 - HEATING Convocatoria de propuestas Data not available Régimen de financiación DEM - Demonstration contracts Coordinador SERMASA Aportación de la UE Sin datos Dirección C/SAN BERNARDO, NR. 64 28015 Madrid España Ver en el mapa Coste total Sin datos
