Reinjection and tracer tests in the Laugaland geothermal field, N-Iceland

Abstract

Water injection into geothermal systems was initiated about three decades ago. In most cases the purpose is to dispose of wastewater for environmental reasons. In other cases, injection is used to counteract pressure drawdown and for extracting more of the thermal energy in place in geothermal reservoirs. Injection is one of the most complex aspects of geothermal exploitation. Therefore, careful planning and research are prerequisites for successful reinjection. One of the more serious problems which may be associated with reinjection is thermal breakthrough. Therefore, tracer tests are often carried out along with reinjection so as to detect the connections between reinjection and production wells, and to predict the subsequent cooling effect of reinjection. A production-scale reinjection experiment was started in the low-temperature geothermal field at Laugaland, N-Iceland in 1997 and will be completed by the end of 1999. Owing to insufficient recharge, the production capacity of the field is limited and the heat stored in the 90-100_C rock matrix can only by used to a limited extent. The return water from the district heating system of the town of Akureyri was used as the source for reinjection. From September 9, 1997 to June 1, 1999, a total of 749,000 m3 of water was reinjected into the geothermal field, about 30% of the production during that time...