Modelling of reinjection into the Laugaland geothermal field, S-Iceland

Abstract

The Laugaland geothermal field is located in southern Iceland. It is a low temperature system, with the temperature of the hot water in the range of 40-97 C. Hitaveita Rangaeinga has been producing hot water from the field since 1982 at an average rate of 20 l/s and a temperature of 98 C. The production has been continuously measured and the water level observed on a monthly basis. The temperature and chemical components have also been monitored. A two dimensional numerical model has been set up by using AQUA - an advanced software for modelling geothermal fields. An excellent matching between calculated and measured data was obtained. The best calculated location of a reinjection well was found to be 600 m to the northeast of the production well LWN-4 along a northeasterly trending dyke which crosses the production field. A 50-60 m water level recovery in LWN-4 would be achieved in 200 days after the start of reinjection with a reinjection rate of 10 l/s. With the temperature of the injected water at 40 C, thermal breakthrough will not reach LWN-4 in 10 years and the temperature decline would be only 2-3 C. Another possible site for the reinjection well was 180 m away from LWN-4, perpendicular to the dyke to the east. Based on the experience from Laugaland, the management of the Tianjin geothermal system in China is discussed. A long term geothermal monitoring programme is suggested in order to provide information for modelling studies and eventually reinjection operation.