Analysis of temperature measurements, well test data and production history of the Botn low-temperature geothermal field, N-Iceland

Abstract

The Botn field is one of five low-temperature geothermal fields in Central North Iceland utilized for space heating in the town of Akureyri. Since 1981 six wells have been drilled in the field, BN-1 and HN-10 as production wells, and BY-4, BY-3, BY-2, and HY-12 as exploration wells. About 29 temperature logs are available from these wells, and the production and water level changes have been recorded since 1981. A pressure transient test was performed in the field in June 1990. On the basis of these data, the thermal characteristics of the reservoir were analysed, and the main feedzones identified. The hot water upflow appears to be from the western part of the reservoir at depth towards the centre of the reservoir at shallow levels (BY-3). Analysis of well test data from the reservoir was done using semi-log, and computerized methods. Comparable results were obtained using both methods. The reservoir has a transmissivity of about 5.3x10-9 m3/Pa-s. The water level history of the reservoir was simulated using a lumped parameter model. The model has a great storage coefficient indicating free-surface storage. Future water level changes were calculated for various production rates showing a very slow future decline. A simple cold water down-flow model was used to simulate water temperature and chemistry changes in well HN-10. According to this model the water temperature of the well will decline from about 80 to 73°C in the next 15 years.