Characteristics of Reservoir Fluid Chemistry from Preliminary Survey and Exploration Assigment Areas in Sumatra Island, Indonesia

Abstract

According to Indonesia’s Geological Agency (2018), Indonesia has geothermal resources of 25.3 GW which are spread along the volcanic pathways, ranging from Sumatera, Java, Bali, Nusa Tenggara, Sulawesi, Moluccas, to Papua. One of the government’s efforts to accelerate the development of geothermal energy is by granting Geothermal Preliminary Survey and Exploration Assignments (abbreviated as PSPE in Indonesian) to business entities. Until now, the government has established 11 areas, most of which are in Sumatera island, i.e. Mount Geureudong (Aceh Province), Simbolon-Samosir (North Sumatera Province), Cubadak and Bonjol (West Sumatera Province), Graho Nyabu (Jambi Province), Tanjung Sakti (South Sumatera and Bengkulu Province), and South Sekincau (Lampung Province). This study analyzes and interprets geochemical properties as observed from water, gas, and isotope samples taken from the surface manifestations in PSPE areas through a comparison between ternary diagrams (which consist of Cl-HCO3-SO4, Cl-Li-B, Na-K-Mg, N2-He-Ar), the diagram of deuterium-18O isotope, and the mixing diagrams of enthalpy vs. chloride. The results will be used to determine the chemical characteristics of reservoir fluids, which include fluid type, fluid origin, fluid chemical properties, fluid processes, reservoir systems, enthalpy, pH, and reservoir temperature estimation.