Natural state modeling of Mataloko Geothermal field, Flores Island, East Nusa Tenggara, Indonesia using TOUGH2 simulator

Abstract

Mataloko Geothermal Field is located approximately 15 km east of Bajawa City in Southern Central Flores Island, Indonesia. The geothermal system of this field is two-phase dominated with steam dominated zone at the shallower part of the field and liquid dominated at the deeper part with temperature of 210°C and 275°C, respectively. From the exploration effort and preliminary study, the possible reserve of this field is up to 62.5 MWe [1]. This study was carried out by numerical natural state modeling using TOUGH2 simulator. The objective of this study is to present numerical modeling of the Mataloko Geothermal Field based on the currently published paper of previous geological, geophysical, and geochemical study, also the actual measurements on the established wells. The model was matched with actual shut-in temperature and pressure measurement on Well MT-3, also mass and heat flow on the conceptual model to achieve natural state condition. The results conclude that the area of the reservoir is up to 10.2 km2 with exploitable reservoir thickness up to 1750 meter. Temperature of the suspected productive deep liquid dominated reservoir is 275°C. The final permeability of the reservoir is ranging from 18-40 mD with exceptional 91.5 mD at the main fault. Furthermore, this study proposes a more accurate prediction specifically on the shallow vapour region. The potential reserve was calculated using Monte Carlo simulation based on the simulation result. Calculated potential reserve is 52 MWe with 90% confidence level (P10). Expansion of 5×10 MWe power plant capacity is suggested by drilling effort to elevation of-1000 to 0 masl through the productive hot deep liquid dominated zone.