Assessment of Geothermal Potential at Ungaran Volcano, Indonesia Deduced from Numerical Analysis

Ungaran volcano is located in the Central Java, Indonesia. Numerical analysis has performed in order to assess the geothermal potential of Ungaran volcano using a 3-D finite difference simulator HYDROTHERM Ver2.2. A conceptual model constructed based on the results of geophysical studies such as gravity, spontaneous-potential, microearthquake, infrared imagery and shallow ground temperature. Deep geothermal fluids have been supplied from below in the central part of the volcano, then change into a lateral flow; part of the geothermal fluid reaches to the ground surface and forms the Gedongsongo fumarole area. The background temperature distributions and mass flux patterns were calculated for 150,000 years to obtain the quasi-steady state. The meteoric water flow pattern demonstrates predominant downward flow, with mass flux varying between 10 g/cmsec up to 10 g/cmsec. The thermal evolution was calculated for up to 30,000 years. The deep geothermal fluids supplied from below in the central part of the volcano has an enthalpy of 1085 kJ/kg (250C) and a mass flow of 230 kg/s to 250 kg/s. In order to estimate the geothermal potential for conventional electric power production, we employed the minimum reservoir temperature is 150C and the performance of reservoir was predicted for 30 years production. Depths of the reservoir are assumed from 0.5 km to 3 km beneath mean sea level. As the result, the estimated geothermal potentials are 2.3 MW up to 40.4 MW depending on different thicknesses of the reservoir.