Well test interpretation and production prediction for well SD-01 in the Skarddalur low-temperature field, Siglufjördur, N-Iceland

Abstract

Recently a tunnel was constructed between Siglufjördur and Ólafsfjördur in central N-Iceland, which passes through the groundwater system in the mountains above the Skútudalur low-temperature geothermal field. Afterwards, the water level in Skútudalur reservoir started to drop. In order to ensure the geothermal water supply for the coming years, a new well named SD-01 was drilled in the Skarddalur field, which is located to the west of the Skútudalur field. After drilling, two step-rate tests and one long term production test were conducted in SD-01 to observe its pressure response to production. The data were analysed by using WellTester, Lumpfit and the multiple rate test method. The permeability thickness of the Skarddalur geothermal system is estimated to be around 10 Dm, the skin factor of the well between –1.2 and –1.5, the productivity index around 5- 6 (L/s)/bar and the reservoir thickness in the range of 200-240 m. The permeability thickness results from the three methods are quite similar. Based on the present long term production and build-up data, a three-tank open model was developed and the reservoir seems to be a combination of an inner confined system and an unconfined recharge system. Using LUMPFIT, the water level was also predicted for the coming 10 years for different production rates.