Geothermal Model of the Lahendong Geothermal Field, Indonesia

Abstract

Lahendong Geothermal Field is tectonically located in the northern neck arm of Sulawesi Island. The field is part of the depression of the Pangolombian caldera with clear structures in the eastern part but relatively open to the west. The depression of the Pangolombian caldera is being one of the most important with respect to the geothermal system in Lahendong. Thermal structures on surface are mostly fault controlled with a dominant NW-SE and NE-SW directions, and are believed to control the permeability of the Lahendong system. The Lahendong geothermal field is hot water dominated system divided into two reservoirs, the Southern and Northern one. A total of twenty three wells have been drilled into these reservoirs. The Southern one has temperatures of 300 to 350oC with dryness about 80%, and the northern one has lower temperatures between 250 to 280oC with dryness around 30%. Three main alteration zones are encountered in this field namely smectite zone, smectite-chlorite and illite-prehnite-epidote zones. The smectite zone is mainly characterized by the appearance of low temperature clay and a layer with resistivity <10 ohmm. The smectite-illite-chlorite zone is characterized by the appearance of an acid layer and illite-prehnite-epidote zone is characterized by the appearance of chlorite, epidote, prehnite, and secondary quartz. The temperature distribution shows that the interesting site for geothermal resource utilization in the field is located in the NW, W, and SW direction of well pad LHD-4 and W and SW direction of well pad LHD-5.