Integrated geophysical methods used to explore geothermal potential areas in Siogung-Ogung, North Sumatra, Indonesia

Abstract

The manifestations of some hot springs in Siogung-Ogung, North Sumatra, Indonesia have increased speculation of likely geothermal sources. Therefore, integrated geochemical and geophysical methods were employed to identify the geothermal prospect of the area. Two-dimensional electrical resistivity and geomagnetic methods were used for the geophysical survey. The geochemical survey used three concentration measurements: geothermometer silica (SiO2), geothermometer Na-K, and geothermometer Na-K-Ca. A Wenner Schlumberger array with a 5-meter electrode spacing was used to acquire the 2-D resistivity data, which was processed using Res2Dinv software. The geomagnetic method was performed with a proton precession magnetometer, and the data were processed using Surfer to produce the magnetic residual map. The 2-D electrical resistivity results show that the area has low resistivity values (1-700 Ωm). The resistivity values from 1 to 100 Ωm could be due to the presence of hot waters in alluvium, and the resistivity values > 400 indicate andesite rock, which can function as a hot water conductor from the source. The magnetic residual map shows geomagnetic values from 150 nT to 360 nT, which infer the potentiality of geothermal within the study area. The geochemical results show that the reservoir temperature is 572 °C. Based on the integrated results, the study area has promising geothermal potential.