Reservoir simulation of Ulumbu geothermal field using TOUGH2 and ITOUGH2 simulator

Ulumbu geothermal field is classified as a natural two-phase geothermal system, located in the south of Mandosawu - Ranakah Old volcanics and Pocoleok, Flores Island. This field produces 4 x 2.5 MW electric power in 2014 until now with temperature between 230-240 °C. This study aims to perform reservoir simulation in the Ulumbu field. The reservoir simulation method aims to determine the reservoir characteristics of the geothermal field. This research used TOUGH2 and ITOUGH2 simulator to simulate the reservoir. The work concept from TOUGH2 is forward modeling while ITOUGH2 is inverse modeling. Both of methods will produce an output. The output of this research is natural state model that was validated by three wells of the actual measurement (pressure and temperature) and heat flow from the conceptual model. A pressure and temperature profiles are very representative with the data in the three wells. The reservoir location is between Poco Leok and Poco Rii (upflow zone) and continues to the southwest (outflow zone) with an average area of 10.5 km². The top reservoir is at an elevation of 500 m, while the depth is up to -2000 m. Reservoir rock has a permeability value of around 10^-14-10^-15 m², porosity value of 8-10 %, density value of 2500 kg/m³, and specific heat capacity value of 900 J/kgK. Temperature distribution results of the natural state model show the hydrogeological profile of the Ulumbu geothermal system. The natural state model is then used to help undertake a geothermal field development scenario, that is, to calculate resource reserves and to make recommendations for subsequent drilling zones.