| Abstract |
Ulumbu Geothermal Field is located in Manggarai District, Flores Island, Indonesia. It is approximately 13 km south-southwest of the city of Ruteng. The geothermal system of this field is a high terrain type. This field is a part of a government program called Flores Geothermal Island aiming to make geothermal energy as the primary energy used for power generation in Flores Island in 2025. Well testing results indicate that this field has a steam cap underlying liquid dominated reservoir with temperatures of 230-240oC. NW-SE faults are the main geothermal conduit of this field, since most surface manifestations, such as hot springs, fumaroles, mud pots, and steaming ground are found along these faults. The objective of this study is to present a natural state model of Ulumbu Geothermal Field based on geological, geophysical, geochemical, and wells data from several published papers. The model was only validated using available temperatures data from three drilled wells because of limited published data. Moreover, the mass and heat flow of the model were also validated with conceptual model to achieve natural state condition. Such condition was achieved by continuous calibration process by adjusting the horizontal and vertical permeability. The final permeabilities of the reservoir are ranged from 25-65 mD. The model indicates that the temperatures, mass flow, and heat flow profiles are well-matched with the actual data, although the room for further improvements is still available. The steam cap underlying liquid dominated reservoir was also successfully modelled, since the simulated well pressure shows a pressure gradient change at about -700 masl. This model is the first natural state model of Ulumbu Geothermal Field and the first geothermal field model in eastern Indonesia that has been established successfully. |