Interpretation of temperature measurements and well test analysis at Sumarlidabaer and a simulation of the Laugaland geothermal system, S-Iceland

Abstract

Sumarlidabaer is one of the low-temperature geothermal fields in southern Iceland, about 80 km south east of Reykjavik. Fourteen wells were drilled in the field in 1983-1987 most of them shallow exploration wells. Well SY-4 is the only production well. The water is used for chicken farming and space heating in the area. After evaluation of all available geological, geophysical and temperature data, the temperature distribution, the location of aquifers and the flow direction of the hot water as well as the inflow of cold water into the system were determined and discussed. The cooling of the water in the production well is of a particular interest. It is now believed to be mainly due to ground water down-flow through wells SY-3 and SIS-5. Analysis of well test data from the Sumarlidabaer reservoir were made using Theis and Horner methods. The reservoir has a transmissivity of about 9x10-8 m3/Pa-s and storativity of about 2.5x10-8 m/Pa. The estimated average thickness of the reservoir is 470 m. The Laugaland low-temperature geothermal field (4 km northeast of the Sumarlidabaer field) was simulated by lumped parameter model using the LUMPFIT computer program. An open two tank model was used to simulate the future response of the reservoir. The results indicate that the Laugaland reservoir has a volume of 1 km3 and is connected to an open system (possibly the ground water system in the area). An open two-tank and a closed three-tank model were used to predict the water level changes during the next ten years for different pumping rates. The optimum pumping rate from the reservoir is close to 15 l/s in order to keep the water level at the present depth.