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Characterization of The Changes In The Reservoir In The Ellidaárdalur Low Temperature Field, Reykjavík, Iceland As A Part of The Result Project
The RESULT project aims to demonstrate the potential for increased performance of geothermal reservoirs for direct heating in urban areas of northern Europe. One of the goals of the project is to enhance the lifetime and heat recovery of such reservoirs. The Ellidaárdalur geothermal area in Reykjavík, Iceland, contains one such reservoir. It is close to a volcanic zone, just a few kilometers west of the Krýsuvík fissure swarm, one of the fissure swarms of the Reykjanes peninsula. The area has been harnessed for district heating since 1968 and has been one of the geothermal fields providing hot water for space heating in Reykjavík and surrounding municipalities. There is a wealth of data relating to drilling, well completion, production history and temperature development available for the area. The production has varied from 1.03 GL/year in 1968 up to a high of 5.65 GL/year in 1983, but since 1983 the production from the field has decreased and in the last 10 years it has been between 1.62 and 2.60 GL/year. Substantial cooling has been observed in the field from the start of production with produced water temperature from wells in the field decreasing from over 100°C in many wells down to around 80°C or even lower in some wells. This has been accompanied by changes in chemical components. In general, the pattern seen in all wells is that the concentration of Cl, CO2, Ca and O2 increases with time as the temperature decreases. The concentration of SiO2 and F decreases with decreasing temperature. The increased oxygen content in the produced water has been an issue, as oxygen causes corrosion of material and equipment. This has led to production from specific wells being decreased or stopped. Temperature measurements taken within the RESULT project in two wells that were sealed with a monitoring tube in 1991 to stop downflow of cold water show that temperature has gradually increased back to original formation temperature values. The data from the field suggests downflow of colder water from shallower aquifers through unused wells has contributed substantially to the cooling in the field, at least since production from the field was decreased. This indicates that the cooling in the field can, at least to some extent, be reversed by changing the production scheme and re-casing and/or sealing more wells.