Assessment of the Kaldárholt geothermal system and associated reinjection into the nearby Laugaland system, S-Iceland

Abstract

The Laugaland and Kaldárholt low-temperature geothermal fields in S-Iceland have been utilized for heating the nearby towns of Hella and Hvolsvöllur since 1982 and 2000, respectively. A conceptual model for the Kaldárholt geothermal system, based on analysis of temperature conditions and geological data includes that an up-flow of 67°C water flows from depth along a NW-SE direction. The results of well tests and interference data analyses indicate that the Kaldárholt reservoir is quite permeable. Calibrated lumped parameter models were used to predict the water level changes for different production scenarios. Based on the predictions, the production potential of the Kaldárholt system is estimated to be about 55 l/s or 95 l/s, for the next 10 years, assuming maximum allowable pressure drawdown of 100 or 240 m, respectively. Water from Kaldárholt has been reinjected at Laugaland at 3-4 l/s since January 2000. According to the cooling predictions based on a tracer test conducted at Laugaland in 1992, the reinjection induced temperature decline of well LWN-4 should be 2-5°C. This is greater than the actual cooling observed, which is less than 1°C at the end of 2002. The discrepancy is mainly attributed to a drastic change in flow conditions because of reduced production since 2000. Major earthquakes in June 2000 may also have influenced the reservoir flow-pattern at Laugaland.