Updating the Complexity of Tompaso Geothermal Conceptual Model, Indonesia

Abstract

The Tompaso geothermal field, located in North Sulawesi, Indonesia, presents a highly complex geothermal system influenced by various geological factors revealed by the recent data. This study updates the conceptual model of the Tompaso field based on new data from the latest drilling campaign and integrates findings on permeability control, hydrology, heat source, and reservoir structure. These updates comply with the general geological setting of Tompaso which is influenced by the Tondano Caldera, formed during explosive rhyolitic and dacitic eruptions, and composed of multiple volcanic formations including pre-, syn-, and post-caldera units. Hydrological features include two major upflow zones, cold water downflows and cold aquifer layers that feed into the system, complicating the temperature distribution across the field. The reservoir's heat source and upflow are believed to be associated with two volcanic zones which are the Rindengan-Sempu complex and possibly near the Umeh-Wowok complex. The economic outflow zone is driven by the permeability in the Tompaso reservoir which is controlled by formation permeability including matrix and fracture, with different zones contributing to the overall flow dynamics. The deeper high-permeable zones are associated with high-intensity fracture zones which are laterally distributed by a formation with similar mechanical properties and more prone to be fractured, while the shallower pores or microfractures-supported in formation permeability dominate in volcanic pyroclastic rocks which consist of ignimbrite and volcanic breccia. The outflow from these two upflow are mixed on the northeastern part of the field, manifesting the thermal fluid on the surface. The reservoir is capped by a thin altered-tuff layer, protecting it from an overlying cold aquifer that is controlled by basaltic lava-dominated formation. Results from the latest exploration and make-up wells and surveys are also presented and integrated to present an overall conceptual model of the field.