| Abstract |
The Wayang Windu Geothermal Field has been in continuous operation for 25 years and has been able to sustain full generation at the power plants with a total installed capacity of 230.5 MWe. This paper discusses the physical and chemical evolution of key surface features during this period of continuous energy production. Among the 11 thermal manifestations identified in the field, it focuses on five thermally active features considered most representative of ongoing evolution: Wayang and Burung Craters, along with three thermal springs—Cibolang, Sukaratu, and MBA Spring. Our findings reveal changes at Burung Crater, where reservoir pressure drawdown has intensified boiling and increased steam dominance, leading to lower gas content. Meanwhile, Cibolang hot spring exhibited a relatively steady geochemical composition, with features suggestive of influence from surface oxidation. Stable isotope analysis (δ¹⁸O and δD) underscores this disparity, with Burung Crater showing notable isotopic shifts while other manifestations remain stable. Despite these localized changes, the broader thermal features in the Wayang Windu Geothermal Field demonstrate remarkable resilience, indicating minimal long-term impact from geothermal development. These insights support more effective management and stewardship of mature geothermal fields by improving interpretation of surface manifestations as indicators of subsurface changes. |