STUDY OF HYDROTERMAL ALTERATION AND WATER GEOCHEMICAL TO DETERMINE FLUID CHARACTERISTICS IN LILLI SEPPORAKI GEOTHERMAL FIELD, WEST SULAWESI, INDONESIA

• Main Author: Putri Pratama, Azshelia
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/69717
• Institution: Institut Teknologi Bandung

The Lilli Sepporaki Geothermal Field is located in Polewali Mandar Regency, West Sulawesi Province. This field is associated with Tertiary volcanic activity. This field has four manifestations of hot springs with temperatures between 60.9oC to 97oC. This study aims to understand the alteration process and fluid characteristics by determining the lithology and alteration below the surface and the geochemistry of water from the manifestations on the surface. This study uses primary data in the form of drill cores drilled from wells LLK-1 and LLK-2 with a depth of 700 m for each well. This study also uses secondary data in the form of water chemistry data on surface manifestations, as well as geological and geophysical data in the research area. The analytical methods used include petrological analysis, petrography, X-Ray Diffraction (XRD), and water geochemistry. The lithology of LLK-1 and LLK-2 is a volcanic product consisting of lapilli tuff, pyroxene andesite, and biotite andesite. All of these lithologies are equivalent to the Eocene Inseparable Volcanic Unit. The alteration process in both wells is in the form of primary mineral replacement and open space filling, with the intensity of alteration in the sample being weak to moderate. The alteration zone in the LLK-1 and LLK-2 wells consists of the smectite-quartz-calcite-chlorite-pyrite alteration zone and the smectite-quartz-calcite-chlorite-pyrite-epidote alteration zone. The veins in the LLK-1 and LLK-2 wells are filled with the minerals quartz, epidote, and calcite. The geothermal system in the research area currently consists of 2 systems, namely the Sepporaki System and the Weighing System. The source of water in these two systems is meteoric water which is heated by the remaining heat from the intrusive rock that is not exposed. The water then comes out as hot springs through the weak fault plane. The Sepporaki Geothermal System has a chloride water reservoir and is partial equilibrium with a reservoir temperature of 170 ± 10°C (with Quartz Geothermometer, Na-K-Ca and Na/K), while the Kaimbang Geothermal System has a chloridebicarbonate water reservoir and is partial equilibrium, has a reservoir temperature of 150 ± 10°C (with Quartz Geothermometer and Na-K-Ca).