Reservoir Identification of Bac-Man Geothermal Field Based on Gravity Anomaly Analysis and Modeling

The Bac-Man gravity modeling was carried out to describe the geological structures that control the geothermal system and estimate the area of the geothermal reservoir. A total of 125 data points were used to produce a complete Bouguer anomaly map of the area. The gravity data are separated into regional and residual components to enhance the structural features of the sedimentary and basement rocks in the study area. Gravity data were analyzed using gradient interpretation techniques for edge detection, such as vertical descent. To perform three-dimensional (3-D) modeling, a 5 × 5 km volume and a depth of 2.5 km were selected. This study presents the interpretation of various gravity anomaly maps and 3-D inversion models. The interpretation of the vertical derivative of the gravity data indicates the presence of a low gradient anomaly. The anomaly map is used to identify several faults or intrusions compared to the faults or intrusions that are mapped. The 3-D model reveals that there are 3 geothermal reservoirs, and the average block density value is 2.25 g/cc. These reservoirs are spread over the Southern area (Cawayan and Tanawon Sector), East area (Boton Sector), and Palayan-Inang Maharang area. Faults or rock intrusions are the limiting factors for the three existing reservoirs. The results obtained from this study will lead to a better understanding of the geothermal system in the study area, in particular, reservoir boundaries, and assist in future geothermal exploration