Updated Geological Framework of Wayang Windu Geothermal Field, Indonesia

Abstract

The Wayang Windu geothermal field is one of the most prominent geothermal fields in Indonesia and has been producing since 2000 with a total installed capacity of 227 MWe. The published Wayang Windu geological model were evaluated in 2006 and focused on facies units and regional structure setting from the analysis of LANDSAT data. In 2021-2022, the geological model is updated with the main objectives of having an updated understanding of the geological framework at the Wayang Windu geothermal field and providing a more robust and updated data feeding for advanced analysis (e.g., static model and numerical reservoir model).

During 2006 to 2021, additional data has been sufficiently gathered, including Light Detection and Ranging (LiDAR) imagery in 2019 and subsurface data from make-up wells drilled in 2012-2021 campaigns. Several initiatives were executed during the geological model update. The LiDAR Digital Elevation Model (DEM) data analysis was performed, aimed at refining the interpretation of volcano-tectonic features and structures lineament. The DEM data shows several conspicuous volcanic centers in Wayang Windu. The combination of DEM data and additional petrographic and XRD analysis of cores and rock cuttings, including paleosol analysis as a key marker has helped refining the formation boundary and allowed definition of seven formation units.

The structures lineament analysis from DEM, combined with the re-interpretation of borehole image logs suggests three structure lineament zones, consisting of areas in the North and South Wayang Windu which are heavily dissected by structure lineament. Whereas the area between those two zones has less structure lineament. A gravity inversion modelling and recent resource observation have allowed the interpretation of intrusion body, completing the updated geological model of Wayang Windu.