Drilling programme for a low-temperature geothermal well using a small rig - case history : Siglufjörður, N-Iceland

Abstract

Geothermal utilisation is categorized into two parts, direct and indirect. Direct utilisation includes the use of hot water for district heating, agricultural purposes and swimming pools where the temperature of the water ranges from 20 to 120°C. This paper describes direct observations of the drilling of a low-temperature well for the district heating system of Siglufjördur (population 1300) in North Iceland that was carried out in August 2010. Several novel methods used for drilling lowtemperature wells in Iceland are also discussed, as they were employed in the actual drilling project. They include: the use of a small highly mobile drilling rig (only four drillers carried out all operations on a small footprint of the drill site); the use of down hole hammers (DTH) for drilling to 300 m; the connection of casings by welding; the delivery of cement slurry in ready-mix cement trucks, pumped with a concrete pump; and the underbalance drilling of the productive formation by using a temporary casing and compressors to reduce formation damage. The undertaking proved a great success as the well only had to be drilled to 702 m rather than the target 1000 m, taking 24 days to complete (working 12 hr. per day). Pump tests confirmed that 30 l/s of 75°C water could be produced from the well, corresponding to 5 MWth of usable heat. The additional water was required to cover future expansion and for back-up reserves. The district heating system is owned by RARIK, the State Electric Power Works. The well was drilled by Jardboranir hf (Iceland Drilling Company Ltd.), and ÍSOR (Iceland GeoSurvey) provided geothermal expertise for site selection, all investigations and logging at the time of drilling.