A Review of the Aluto Langano Geothermal Project and Recent Temperature and Pressure Logging

Abstract

The Aluto Langano geothermal field covers an area of at least 8 km2 in the central part of the Aluto volcanic complex, a rhyolitic volcanic field in the main Ethiopian Rift Valley. The first two wells drilled south and west of the complex penetrated through a low temperature outflow. The last six wells drilled in the complex, and centered on the Wonji Fault Belt found temperatures of 200 to 334 oC. Four of these wells have been used for production and one for injection. High temperatures are offset by low to moderate permeability. A 7.28 MW net power plant operated briefly but was shut down due to numerous power plant and resource problems. Efforts have now been underway for one year to refurbish and restart the power plant. Caliper logging has shown that the two hottest production wells are in good mechanical condition. One cooler well is largely blocked by carbonate scale and the other cooler production well, which still has a good flow rate, has a major blockage at a depth of 701m. New precision digital temperature and pressure logs agree well with many older mechanical logs and show new details regarding permeable intervals in the wells. Pressure logs show very large downhole pressure drops when the hottest wells are flowed, which is in agreement with past interpretations of these wells having low permeability.