Abstract
The discharge fluid in a single vapor phase from the exploration well MT-2, drilled to a depth of 162.35 m in the Mataloko geothermal field, Flores Island, Indonesia, is relatively low in non-condensable gas content (0.61 -0.69 wt%) and its gas component is predominant in CO2 (91 mole%). The discharge steam is thought to be derived from a liquid water dominated reservoir existing at a deeper level. Isotopic compositions of hydrogen, oxygen, carbon, sulfur and helium, and chemical composition of minor gases in the discharge fluid from the well MT-2 suggest that its water vapor (H2O) consists of mainly meteoric water affected by magmatic water or water-rock interaction, while the gaseous components originate mainly from magmatic fluid. Based on several chemical and isotopic geothermometers and measured bore hole temperatures of the well MT-2, the subsurface temperature is estimated to be 192 -230 °C at the shallow steam-dominated reservoir and 270-306 °C at the deep water-dominated reservoir. The discharge steam from the exploration well MT-1 and fumaroles, which are located within 200 m from well MT-2, shows chemical characteristics similar to well MT-2. It suggests that they are derived from a common source, that is a deep water-dominated reservoir possibly having a relatively large extension in the Mataloko field.
