MSc defence by Julia Satriani

Julia Satriani Alibazah from Indonesia, MSc Fellow in Geology at University of Iceland will present her MSc project on on Thursday 26th of September at University of Iceland, Askja building at University of Iceland, Askja building, room announced later on.  The presentation will be a part of the UI series "Open seminar at Masters-day of Natural Sciences".  

The title of the project is:
Evaluation of acid alteration in Sikidang Area, Dieng Geothermal Field, Indonesia

Julia's supervisors are:
Eniko Bali, Professor in Mineralogy and Petrology, School of Engineering and Natural Sciences, Faculty of Earth Science, University of Iceland, Iceland
Iwona Galeczka, Laboratory supervisor in Geochemistry, School of Engineering and Natural Sciences, Faculty of Earth Science, University of Iceland, Iceland

Her external examiner is Daði Þorbjörnsson, Senior Geothermal Consultant, ÍSOR

Abstract
The southern part of the Dieng geothermal field, the Sikidang area, has been explored since 1977, with 27 wells drilled by 1995; however, these wells are currently non-productive, partly due to acidic fluid indication. This study investigates the subsurface geology of five selected Sikidang wells to determine the extent of acid fluids and characterize hydrothermal alteration processes. Samples of drill cuttings and silica scale were analyzed using stereomicroscopy, petrography, SEM-EDS, Loss on Ignition, ICP-OES, fluid inclusion microthermometry, Raman spectroscopy, and LA-ICP-MS, complemented by deep liquid calculations and saturation index modeling using WATCH and PHREEQC. Sikidang area is characterized by andesite lava, andesite tuff, tuff breccia, and andesite breccia. Subsurface lithostratigraphy comprises Young Sikidang Volcanics, Sikidang Volcanics, Bisma Volcanics, Old Dieng Lava, and Andesite Complex. Petrographic analysis reveals variable hydrothermal alteration: JS-1 exhibits acidic alteration with alunite and sulfur and high-temperature minerals at depth; JS-2 and JS-5 show neutral pH alteration; JS-3 contains native sulfur at shallow intervals. Casing corrosion corresponds to acidic alteration in JS-1 and JS-3, whereas JS-2 and JS-4 are mainly affected by mechanical factors. Fluid chemistry of the reservoir calculated from wellhead composition indicated near-neutral reservoir with pH 4.2-5.2 at temperatures 236 to 321°C. Deep liquid calculation corrected with fluid inclusion compositions obtained by LA-ICP-MS reveal more acidic fluids with pH 1.8-3.2. Thermal evolution assessed via fluid inclusions and mineral geothermometry indicates near-equilibrium conditions in JS-1 and JS-5, whereas JS-2 shows slight thermal variation. Maximum reservoir temperatures reach 327°C, suitable for geothermal exploitation, although acid alteration and elevated non-condensable gases present operational challenges.