GEOLOGY AND FLUID GEOCHEMISTRY OF RANTAU DEDAP GEOTHERMAL SYSTEM, SOUTH SUMATRA

• Main Author: Mussofan, Wildan
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/70627
• Institution: Institut Teknologi Bandung

Exploration and development activities in Rantau Dedap geothermal field provides geology, geochemistry and geophysics data. These data have not yet integrated interpretation. Analysis of LiDAR (light detection and ranging) and geologic maping data are performed to generate geomorphology and geology map. The integration of geology map and subsurface geology are performed to generate geology model. Geochemistry analysis of water, gas and stable isotope (?18O and ?2H) are performed to understanding composition, type, maturity, origin and source of reservoir. Hydrothermal fluid flow pattern and processes inside the reservoir are explained in geochemistry model. The objective of this research is generating a tentative geothermal model by the integration of geology, geochemistry and geophysics models to understanding the Rantau Dedap geothermal system comprehensively. Rantau Dedap geothermal system has the heat source i.e. hot intrusive rock beneath the eruption center of Mount Bukit Besar. The main reservoir is hosted at dacite and rhyolite tuff. The permeability of reservoir is controlled by combination of stratigraphic contact and structure. Reservoir fluid is mature chloride water formed by meteoric water origin. Reservoir fluid has 1026 to 1710 mg/kg chloride content and neutral pH 5,4 to 6,6. Geoindicator Cl, Li and B data shows the reservoir fluid come from more than one reservoir sources. Based on well temperature, the reservoir has temperature ranging from 247 to 2960C at the main production area. Rantau Dedap geothermal system has two main reservoir sectors and upflows. Reservoir Sector I has the upflow zone close to L1ST and L3 wells. Reservoir Sector II has the upflow zone close to I2, I3ST and M3 wells. From these locations, parent fluid is traveling to the marginal wells i.e. I1, M1, M2ST, M4 and L5ST. Residual fluid continuously flow into wells within the outflow zone i.e. C1, C2, B1 and B2. Boiling and dilution process is occurred during the parent fluid is traveling from it sources. Both of this reservoir sector is connected by NE-SW fault. Another potential parent fluid is found close to N1ST well. MT profile shows the existence of conductive layer (< 20 ohm) at the shallow depth, however the current clay cap of Rantau Dedap geothermal system is controlled by lithologic unit Subaqueous Debris Flow.