HYDROTHERMAL FLUID EVOLUTION OF RANTAU DEDAP GEOTHERMAL FIELD, SOUTH SUMATRA

• Main Author: Sakinatul Hasanah, Lara
• Format: Theses
• Language: Indonesia
• Subjects: Geologi, hidrologi & meteorologi
• Online Access: https://digilib.itb.ac.id/gdl/view/79575
• Institution: Institut Teknologi Bandung

This research was conducted to determine the fluid evolution in the active production wells, namely RD-I2, RD-L3, and RD-M3 of the Rantau Dedap Geothermal Field. This study compared the characteristics of ancient hydrothermal fluid and the current fluid flow from the wells. The ancient fluid characteristic was determined from the distribution of hydrothermal alteration minerals obtained by petrography, X-Ray Dif raction (XRD), and Methylene Blue (MeB) analysis. The current fluid characteristics were identified by chemistry analysis of water samples that flow out from the well. The data used include 15 drill cuttings samples, 26 thin section samples of cuttings, four thin section samples of core, 10 XRD analyses by clay mineral preparation method, water chemistry, and MeB of well data. Based on the results of petrography, XRD, and MeB analyses, the subsurface hydrothermal alteration zones in the three wells were classified into four, namely Alteration Zones of Smectite, Chlorite+Calcite±Anhydrite, Chlorite+Epidote, and Ilite+Epidote. The ancient top of geothermal reservoir (ToR), determined from the first appearance of epidote at elevation of +1,300 to +1,350 m, and in well RD- M3, it deepened to elevation of +1,270 m. The reservoir fluid had temperatures of 200-250°C, even at 280°C, and neutral pH. The processes in the ancient hydrothermal fluids were boiling, mixing, condensation, and neutralization. The characteristics of the current reservoir fluid are fully equilibrium alkaline chloride water. The temperature and pressure measurement shows that the current reservoir fluid has temperature of 255-260°C with ToR at elevation of +800 to +1,100 m elevation. The hydrothermal fluid is still boiling, especially in wells RD-I2 and RD-M3. The evolution of the hydrothermal fluid shows a deepening of ToR. The hydrothermal fluid also cools and becomes more alkaline.