GEOLOGY AND FRACTURE ANALYSES STUDY FOR IDENTIFICATION OF GEOTHERMAL SYSTEM AND BOUNDARIES DELINEATION IN SOUTHERN NGADA FIELD, NUSA TENGGARA PROVINCE

• Main Author: Pradipta, Devito
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/64046
• Institution: Institut Teknologi Bandung

Southern Ngada Geothermal Field is located in active magmatic arc, therefore it has potential to form a volcanic type geothermal system. The previous study had conviced that Southern Ngada Field was consisted of one geothermal system, however the presence of manifestation clusters which is scattered in different volcanic morphologies raises a pressumption that different geothermal systems for each manifestation clusters and volcanic morphologies might be present. This research aims to identify the sum, type, and characteristics of geothermal system, natural fracture characteristics, generate a conceptual model, and delineate each system boundary. This research was conducted through integration of geological study and fracture characterizations in the research area. The geomorphological analysis and DEMNAS image study showed that Nage Manifestation Cluster is associated with Nage Caldera and Wolo Piu Crater, while Keli-Bena Manifestation Cluster is associated with Bena Crater and Wolo Puti Cluster is associated with cinder cones. Those different associations of manifestation cluster with its volcanic morphology were proven through volcanostratigraphic observation, which showed difference associations of each manifestation clusters with volcanostratigraphic units. Fluid manifestation geochemistry showed volcanic water type in Nage Cluster, while volcanic and condensate water type in Keli-Bena Cluster with mixing processes with meteoric and magmatic fluid. Hydrothermal alteration zonation also showed indication of three sources of hydrothermal fluid which was sourced from different heat sources. Hydrological pattern of all manifestation clusters showed difference of local groundwater flow pattern so that there were different hydrological setting in each cluster. All compiled analyses proved the presence of three geothermal system: Nage System, Keli-Bena System, and Wolo Puti System. Structural geology analyses and natural fracture characterization were done in each identified geothermal systems to prove the difference of structural geology setting and fracture characterization for each system. Structural geology analyses showed that Nage System is on PDZ fault, while Keli-Bena System is on antithetic fault and Wolo Puti System is on extensional structure. Fracture characterization of Nage System showed higher intensity, density, fractal dimension, and porosity-permeability estimation than Keli-Bena System. Conceptual Model of Southern Ngada Geothermal Field showed role of F3 fault as a barrier between Nage System and Keli-Bena System. Boundary of each geothermal system were delineated based on volcanostratigraphy aspects, structural geology, and hydrothermal alteration which were further validated by resistivity data from magnetotelluric surveys. The result of this research concluded that the research area consists of three different geothermal system with different structural geology setting and fracture characteristics. The identified geothermal system boundaries could be delineated through volcanostratigraphy, structural geology, and hydrothermal alteration. The presence of three geothermal systems in the research area were validated by resistivity data from magnetotelluric survey.