INTERPRETATION OF GRAVITY METHOD IN IDENTIFYING GEOTHERMAL POTENTIAL IN BONJOL AREA, PASAMAN REGENCY, WEST SUMATRA

• Main Author: Ihsan, Faizul
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/81181
• Institution: Institut Teknologi Bandung

Indonesia's geothermal potential has a tremendous opportunity to fulfill domestic energy needs. One of those potentials is the Bonjol geothermal area located in Pasaman Regency, West Sumatra Province. To identify the geothermal potential, gravity measurement data from an integrated survey conducted by The Integrated Survey Team of Pusat Sumber Daya Geologi (PSDG) in 2007 was used with supporting data, which included geological, geochemical, and other geophysical methods. In this research, the gravity measurement data is reprocessed into a complete Bouguer anomaly calculation using an average density of 2.65 gr/cm3 which is then generated into a complete Bouguer anomaly map. In the subsequent step, the Bouguer anomaly is separated into regional and residual anomalies using the Gaussian filter method and a combination of the Gaussian filter method with BEMD (Bi-Dimensional Empirical Mode Decomposition). The regional and residual anomaly values obtained from both methods have similar ranges and trends and share a northwest-southeast orientation. The regional and residual anomaly values obtained from both methods have similar ranges and pattern trends and both have a northwest - southeast orientation. From the residual anomaly maps obtained, the residual anomaly map resulting from the combination of the Gaussian filter method with BEMD was selected because it is more in line with the identified surface geological conditions and has a northwest - southeast and northeast - southwest oriented lineation pattern, and also better fits the identified geothermal manifestations on the surface. Furthermore, 2.5D forward modeling is carried out on the selected residual anomaly trajectory data, assisted by the results of derivative analysis using the Second Vertical Derivative (SVD) method supported by geological data, geochemistry, and other geophysical methods to produce subsurface modeling. From the modeling, it can be identified that the geothermal system in the Bonjol area consists of a reservoir in the form of sedimentary rocks of the Sihapas formation starting at a depth of 900 meters, then the cap rocks are lava tua and lava Malintang rocks and the heat source is estimated to be an intrusion of rocks under the Sungai Takis and Sungai Limau springs. The water in the reservoir comes from meteoric water that comes out through faults, resulting in upflow and outflow zones.