Heat Source Movements in Lahendong Geothermal Field and Its Affect to the Reservoir Characteristics

Abstract

Active plates tectonic zone in northern Indonesia has formed series of active volcanoes on the northern island of Sulawesi and Maluku archipelago. Lahendong geothermal system is located in center of G. Lengkoan, G. Tampusu and G. Kasuratan and was formed at ranging from 2.2 million to 0.5 million years ago. Lahendong geothermal field is located at elevation of 750 to 1000 masl. Until 2013 there are 29 wells drilled from 10 clusters with depth of well varies between 1200 to 2500 m. Currently in the Lahendong field has intalled power plants with total capacity of 80 MWe. The reservoir produces two phase fluid, but sourthern part of the reservoir has lower water saturated than northern. Specially, reservoir beneath Linau Lake produces the biggest producer steam (up to 20 MWe), but unfortunately the fluid is highly acidic. Research of heat source activities by using Geothermometer mineral marker such as chlorite, actinolite, epidote, wairakite and smectite from rocks cutting and cores taken from the wells indicated that there were occured three times of heat sources shifting.Which are started moving from Kasuratan to Pangolombian, then moving toward Linau Lake and the last back again to Kasuratan. The evolution of heat sources possibly related to the regional tectonic activities in the regional area, and that greatly affect to characteristics of the reservoir of Lahendong field. Heat dispersal patterns showed the highest temperature is in the southern part (area of Linau and Kasuratan) and towards eastern part (Pangolombian) temperature decreases. Base on data of water levels and pressures in the reservoir, indicating a structural barrier separates into two areas between Linau and Kasuratan.