Evaluation of recent temperature and pressure data from wells in Tendaho geothermal field, Ethiopia and from well HG-1 at Hágöngur, Iceland

Abstract

The Tendaho geothermal field is a geothermal prospect area in N-Ethiopia, which has both shallow and deep wells. Detailed analysis of downhole temperature data from the wells shows that the hottest part of the well field is in the vicinity of well TD5. The reservoir pressure is also at maximum in the same area suggesting an upflow zone near well TD5. Data from short term production tests of wells TD5 and TD6 were analysed. The results of well TD5 discharge indicate an average thermal output of 24.5 MWt at 18 bar-g wellhead pressure. This suggests that TD5 is capable of producing 2.4 MW of electricity. Generally, the wellhead pressures are stable at well shut-in conditions except for wells TD5 and TD6. TD5 showed rising wellhead pressure in 2002 and 2003. Hágöngur is a geothermal area located in Central Iceland. Surface exploration started in 1995 with a reconnaissance geological survey and mapping of the geothermal manifestations because of plans to construct a hydro dam in the area. The studies suggested the presence of a central volcano, and a semi-circular alignment of rhyolitic domes implies the possibility of an underlying caldera. A transient electromagnetic (TEM) resistivity survey indicates a subsurface high-temperature geothermal anomaly in an area covering 20-40 km2. Sampling and analyses of gas and fluid from geothermal manifestations indicated sub¬sur¬face temperatures up to 290°C. The first well, HG-1, was drilled to 2360 m depth in 2003 in the central part of the anomaly. The observed bottom hole temperature is over 310°C.