HYDROTHERMAL FLUID EVOLUTION OF CANDI UMBUL-TELOMOYO GEOTHERMAL AREA, CENTRAL JAVA

• Main Author: ULINUHA ANNISA (NIM: 22015310), HISKIA
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/27882
• Institution: Institut Teknologi Bandung

<p align="justify">The geothermal system in Candi Umbul-Telomoyo is estimated to be related to the youngest volcanic activity of the Telomoyo complex. Based on relative content of Cl-Li-B and resistivity data, the research area is interpreted to have two different reservoirs, i.e. Candi Dukuh and Candi Umbul reservoir. The estimated temperature of Candi Dukuh reservoir is 210 - 230oC (Na/K geothermometer), while temperature of Candi Umbul reservoir is 230 - 250oC (Na/K geothermometer). Top of reservoir based on MT data is estimated at elevations of -1000 m. Alteration in CTL 1 and 2 wells shows a change in reservoir fluid. <br /> <br /> The methods used in conducting this study are petrography and X-Ray Diffraction (XRD) analysis to define lithologies, hydrotermal alteration minerals, and clay minerals. Fluid inclusion study is used to get the temperature of homogenization (Th) of fluid in vein mineral. <br /> <br /> The subsurface conditions in the study area are divided into two zones based on alteration minerals, namely the caprock and reservoir zones. The caprock zone was at elevation of 700 - 200 m at depth, with fluid temperatures of 120 - 180oC and a slightly acidic pH. This zone is characterized by the presence of clay minerals, such as kaolinite and smectite. While the reservoir zone was at elevation of >200 m at depth and had temperatures of 260 – 330oC and neutral pH. This zone is characterized by presence of epidote. <br /> <br /> In the study area, there are three changes in fluid characteristics occurring during the past until now, such as the changes in chemistry fluid, reservoir temperatures and elevations of caprock and reservoir zones. The results of chemical analysis based on alteration mineral and the present reservoir conditions show a decrease in Ca concentration and increase in K and Na concentrations. This is probably due to the intensive rock and fluid interaction process which is then followed by the mixing process with meteoric fluids is evidenced by the decrease in temperature that occurs in caprock and reservoir zone. While from the difference in elevation, there is a caprock thickening and a decrease in top of reservoir. This is probably due to the presence of condensate fluid in caprock which has a higher density mixed with meteoric fluid so that the condensate fluid becomes down to the reservoir.<p align="justify">