GEOTHERMAL DRILLING AND WELL PUMPS
Geothermal drilling in Iceland started in 1930 to enhance the natural discharge of geothermal springs that were exploited for house heating. Initially the wells were self flowing (artesian) but in 1964 the fist deep well pumps were installed which allowed much higher production rates and new areas to be tapped. The geology of Iceland is characterised by sequences of basaltic lava flows and an active volcanic zone passing through the centre of the island from SV to NE. Outside the volcanic zones there are the so called low-temperature areas where the temperature gradient is 70-100°C/km but associated with the volcanic centres are the high-temperature fields with temperatures exceeding 300°C at 2 km depth. The paper describes the drilling technology applied in tapping these geothermal resources and the main challenges. Now most wells are drilled of bigger diameters than in the past to take advantage of larger flows and directional drilling is becoming widespread to minimize the environmental impact and to better target the near-vertical structures that conduct the fluid. The well designs have been standardized and together with uninterrupted drilling year after year the drilling technology has advanced. Exploration wells and shallow production wells are drilled with air hammers. Deeper wells are drilled with tricone bits with water as the drilling fluid. Drilling mud is only used to improve the cutting removal when drilling with large bits. Highly automated rigs with top-drives together with down-hole mud motors have allowed much faster drilling. It typically takes 35-45 days to complete wells to 2000 m. Although new technology is important the knowledge and experience of the drilling crew is essential in achieving success. Pumping is required in most low-temperature wells but the hightemperature ones are self-flowing. In many cases the maximum flow is limited by the pump diameter that can be installed inside the well. In Iceland the average pumping rate per well is 40 1/s and the maximum 90 1/s. There are some 200 well pumps installed in the city owned district heating systems and an equal number in rural areas. The large pumps are shaft driven but submersible pumps are used in the smaller wells serving rural areas. The Icelandic geothermal pump evolved after 1964 where the challenge was to obtain long life of the shaft bearings. Now these pumps work for 5-10 years without requiring maintenance. Submersible pumps are gaining popularity as higher temperature motors and of larger size become available.
Sverrir Thorhallsson
Iceland GeoSurvey ISOR Grensasvegur 9 IS-108 Reykjavik ICELAND
国际会议
Workshop for Decision Makers on Direct Heating Use of Geothermal Resources in Asia(亚洲地热资源直接利用国际研讨会)
天津
英文
403-415
2008-05-11（万方平台首次上网日期，不代表论文的发表时间）