A 3D GEOLOGICAL MODEL AND NATURAL STATE SIMULATION OF JABOI GEOTHERMAL FIELD, NANGRO ACEH DARUSSALAM, INDONESIA

Abstract

This project aims to develop a comprehensive numerical model of Jaboi geothermal area which represents the subsurface permeability structure, heat, and fluid inputs of the real reservoir with reasonable accuracy by utilizing the published data. A new 3D geological model developed in LEAPFROG Geothermal and a new natural state model simulated using AUTOUGH2 are presented. Jaboi geothermal field has been explored since the 1970’s, however, no previous studies have gone as far as creating a 3D geological model or a numerical model of the area. The construction of the new 3D geological model of Weh Island was carried out using a compilation of geoscientific data derived from exploration activities of the Directorate of Geothermal, Ministry of Energy and Mineral Resources during 2005-2006. The 3D geological model describes the features such as the geological structures, water level, rock types, and surface manifestations. This model is then used as the basis for developing a new reservoir model, whose grid is 19.2 km in length and 17.6 km wide, with a total of 21,141 blocks. The model domain covers the entire island and extends from the surface to depth and uses an air-water equation-of-state. The simulation was run until steady-state conditions were reached and the model was calibrated using the field data. The best-calibrated model shows the upflow area is adjacent to the fumaroles (FJB-1 and FJB-2) and acidic hot springs (APJ-1 and APJ-2). The temperature of the upflow zone in this model also fits with the geothermometer prediction of values ranging from 250-300oC. This match is achieved by assigning a deep upflow of 36 kg/s of hot water at an enthalpy of 1,400 kJ/kg into four blocks of the Bangga fault beneath Mt Leumo Matee.