Abstract

The Lahendong Geothermal Field lies in the northern part of Sulawesi Island about 30 km south of Manado City. It is located on the edge of the 20 km long Tondano Volcano-tectonic depression which formed in the Pliocene period. The field is centered on the small caldera of Pangolobian which collapsed the central part of the volcanic complex of Tampusu-Linau. Reconnaissance studies and detailed exploration surveys were used to delineate a very large geothermal potential which has been proven by drilling five deep wells. Surface and sub-surface data, including geological logs and production tests, were analyzed to define the main characteristics of this geothermal field and to build a preliminary geothermal model. The model postulates the presence of two water dominated reservoirs separated by a silicified zone.

The upper reservoir, has an area of about 5 square kilometres and is situated between 400 and 900 m depth in ignimbrites. The reservoir fluid is acidic water with a temperature of 260°C.

The lower reservoir, located below 1500 m depth is about 20 square kilometres in area and occurs in a volcano-sedimentary formation. The reservoir fluid is a neutral water with a temperature around 300 – 350°C.

Investigations are continuing in order to delineate the most suitable location for a 55 MWe power plant as the first phase of development.