| Abstract |
Pertamina has explored the Ulubelu geothermal prospect in southernmost Sumatra, with extensive geological, geophysical, and geochemical surveys since 1989; the surveys indicated the potentially productive area cover over 50 km2. The regional and topographic distribution of hot springs and fumaroles, and drilling results from three slim holes 900 to 1200m deep suggest that there is a liquid dominated reservoir overlain by a steam zone. The slimholes encountered temperatures as high as 210?C in hydrothermally altered andesite rocks. Numerous geochemical and mineralogical temperature indicators suggest the shallow part of the reservoir has recently cooled from 260-300?C to 210-225?C. The heat source for the reservoir appears to lie beneath either Mt. Rindingan in the northern part of the area and/or Mt. Kukusan in the southern part of the area. Development of the Ulubelu prospect has been temporarily stopped by the Indonesian economic and political crises. Within the next five years, it is anticipated that development work will recommence at Ulubelu. |