Subsurface Modeling Based on Gravity Data of Rendingan-Ulubelu-Waypanas (RUW) Geothermal Field, Lampung, Indonesia

Abstract

Indonesia is located along the archipelago which has abundance of volcanoes along the arc. Therefore, Indonesia has a very high geothermal energy potential, such as the Rendingan-Ulubelu-Waypanas Geothermal Field in Tanggamus Regency, Lampung Province. Geophysical exploration is required to characterize the subsurface geothermal system. One of the methods that can be used is gravity method. The data used in this study is an analog Rendingan-Ulubelu-Waypanas Geothermal Field Complete Bouguer Anomaly Map of 2005. The analog map was then converted into digital map for further data processing. Separation of regional and residual Bouguer anomalies has been performed using moving average and spectral filter methods, in which the spectral analysis was conducted in 1D and 2D. The value of Bouguer background density used for 2.5D subsurface modeling is 2.67 g/cc. The gravity anomalies obtained in this study can be interpreted as follow. The existence of high anomalies under Mount Waypanas was interpreted as a Tertiary intrusion of granite with a density contrast of 0.22 g/cc. While low anomalies in the northern part was interpreted as a Quaternary intrusion of diorite with a density contrast of -0.22 g/cc, which acts as the heat source of the system. The reservoir of the system is the Quaternary young volcanics exposed on the surface with averaged thickness of 1500 m. We concluded that the fluid flow in this geothermal system is the meteoric water from Mount Rendingan and Mount Tanggamus, which has a higher topography, flows to a lower topography area in the Mount Waypanas, The fluid flow also creates an upflow under Mount Rendingan.

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“…Way Panas Geothermal Field is associated with the active Sumatera Fault Zone. Moreover, Permatasari et al (2019) conducted gravity modeling in the Rendingan-Ulubelu-Way Panas Geothermal Field Area, Lampung. According to this research, the high anomaly under Mount Way Panas was interpreted as a tertiary intrusion of granite rocks, while the low anomaly in the northern part was interpreted as a quarter diorite intrusion, which was interpreted as a heat source.…”