Fluid inclusion study on the wells MT-1 and MT-2 in the Mataloko geothermal system, Indonesia

Abstract

Fluid inclusions from the wells MT-1 and MT-2 in the Mataloko geothermal system were studied microthermometrically and geochemically. The microthermometric data show that homogenization temperatures of the fluid inclusions at the bottom of the well MT-1 are concordant to the thermal structure estimated from other geological and geochemical data of Mataloko. However, those at the bottom of the well MT-2 are 20-30°C higher than the estimated present temperature (200 °C ). Salinities of all the fluid inclusions are very low. Semiquantitative gas analysis for fluid inclusions from the bottom of the well MT-1 indicates that the inclusions consist mainly of H2O with trace amounts of CO2 and CH4. These data imply that the fluid inclusions were probably formed by trapping steam-condensed water at 220-235°C with small amounts of the gases at a shallow level in the geothermal system. Comparison of the homogenization temperatures to the boiling point curve of water for the well MT-2 suggests that at least 100 m have been eroded from the Mataloko area sinee the geothermal activity began.