Geochemical Reservoir Compartmentalization at Muara Laboh Geothermal Field, Indonesia

Abstract

Ten production wells were drilled and tested at the Muara Laboh Geothermal Field, Indonesia from three well pads during the exploration and the 80MWe development drilling campaigns in 2012-2013 and 2017-2018, respectively. Chemistry of fluid samples were collected from all production wells for liquid, gas and isotope analysis during production testing. Fluid chemistry and reservoir engineering data indicate a geochemically compartmentalized two reservoir systems. The northeast (NE) reservoir sector is characterized by a steam cap with excess steam underlain by high temperature (240-250°C) mature neutral chloride liquid with pH~7, chloride content of ~1600 -1700 ppm, low gas content 0.5 – 0.8wt%. In contrast, the southwest (SW) reservoir sector is deep, very high temperature ( more than 290°C), neutral dilute steam-heated liquid-dominated reservoir with lower chloride content 300 - 500 ppm. Compartmentalization is further supported by different Cl/B ratios, stable isotope signatures, and a substantial temperature gradient of ~70°C within 500 m between the two nearest wells completed in the NE and SW sectors. The distinct fluid chemistry and thermal characteristics of each reservoir sector suggest that there are two poorly connected reservoir compartments In the Muara Laboh Geothermal Field.