| Title | Conceptual Model of the Ijen Geothermal Field, East Java: Indonesia's First Developed Blind Geothermal System |
|---|---|
| Authors | Ryan Libbey, Isto Saputra, John Murphy, Munazyi Husein, Fikri Dermawan, Dalmathias Archady, Rizal |
| Year | 2026 |
| Conference | World Geothermal Congress |
| Keywords | |
| Abstract | The Ijen geothermal field is a high-enthalpy, caldera-hosted system in East Java. The system is liquid-dominated with a two-phase region extending from +200 to +750 mRSL. The ~1.5 km2 upflow of the system is characterized by a >300°C, neutral pH, ~0.3 wt% TDS Na-Cl fluid, with ~0.15-0.3 wt% dissolved NCG in the deep reservoir. The resource is situated within the Pleistocene Kendeng Caldera, in the vicinity of numerous intracaldera volcanic features. One such feature, the Kawah Wurung maar, is adjacent to the upflow at Ijen and is interpreted to be a source of pronounced recharge into the system – resulting in steep lateral thermal gradients between wells. The resource area is devoid of active or fossil surface manifestations despite the occurrence of a relatively shallow boiling >300°C resource. This absence of surface features is the result of a deep (250-300 m) water table and the scrubbing of upward migrating steam and gas by shallow groundwater aquifers that flow laterally across the top of the argillic alteration zone. A sequence of competent and relatively unfractured Holocene lavas in the shallow stratigraphy at Ijen may also influence the lack of manifestations. The exploration and development drilling campaigns conducted by the Medco-Ormat joint venture in 2020-2024 achieved industry-leading results, with 9 of the 10 well legs exceeding their production/injection success thresholds. The conceptual model-driven approach to exploration implemented at Ijen was a key factor in achieving this success. The 34.5 MW Ormat two-phase binary plant at Ijen began commercial operations in February 2025. |