Numerical modelling of Lahendong geothermal system, Indonesia

Abstract

Lahendong geothermal field is one of the most promising geothermal areas in Indonesia. The first 20 MWe Unit started production in June 2001 and is supplied by about 40 kg/s of two-phase geothermal fluid. Today, the power plant is being developed for two additional 20 MWe units, II and III, that are scheduled to be commissioned in 2007 and 2008. This paper describes the development of a detailed numerical reservoir model of the geothermal system underlying the Lahendong geothermal area. The purpose of this study is to review the reservoir engineering aspects of the field and develop a numerical model, based on pressure and temperature data and well output. The TOUGH2 simulator was employed and coupled with interface software developed by Pertamina. Temperature and pressure profiles in the Lahendong geothermal field were studied and their interpretation supports the existing conceptual model of the Lahendong geothermal reservoir. The numerical model was used to calculate a future forecast production of 60 MWe to the year 2036, resulting in a 10 bar reservoir pressure drawdown. The forecast results are, however, uncertain due to a lack of pressure drawdown data, which are essential for model calibration.