The Salak Field, Indonesia: On to the next 20 years of production

• Published in: Geothermics 2020-01, Vol.83, p.101715, Article 101715
• Main Authors: Golla, Glenn U., Julinawati, Tri, Putri, Risa P., Nordquist, Gregg A., Libert, Frederick T., Suminar, Aquardi R.
• Format: Article
• Language: English
• Subjects: Capacity factor; Computer simulation; Decision making; Drilling; Effective fractures; Fractures; Geothermal power; Geothermal resources; Injection; Injection breakthrough; Marginal recharge; Mathematical models; Monitoring; Natural recharge; Non-Condensable gases; Permeability; Realignment; Reservoir management; Reservoirs; Resource management; Salak; Saline water; Steam; Turbines; Wellbore scale
• ISSN: 0375-6505; 1879-3576
• DOI: 10.1016/j.geothermics.2019.101715

The Salak Geothermal Field is the largest producing geothermal field in Indonesia with an installed power generation capacity of 377 MWe. After more than 23 years of commercial operations and through vigilant resource management, the Salak Field is still performing well. Since 1994, when commercial production started, the net capacity factor has averaged about 91% annually. After the last turbine uprating in 2005, the net capacity factor has improved to an annual average of 95%. By 2019, a substantial injection realignment will be implemented which will move all condensate injection outside the field production boundary and shift most brine injection outside and to the southeast margin. This project will mitigate brine injection impact to the AWI 7 and 8 wells and hasten development of the steam cap in the western portion of the field. With this injection realignment, reservoir simulation forecasts show the Salak geothermal resource will likely be able to continue steam production at its current level in the foreseeable future. Similar to other long-producing geothermal fields, Salak has encountered resource management challenges, such as, injection breakthrough, influx of marginal recharge, wellbore scaling, and production of significant amounts of non-condensable gas (“NCG”), in response to commercial production. To address these challenges, an extensive reservoir monitoring program and integration of new make-up drilling results enabled updates and fine-tuning of the conceptual model of the field. Key updates include increased understanding of the distribution of the producing effective fractures and their permeability in the reservoir, identification of injection capacity outside the commercial field boundary in the Cianten Caldera, and improved understanding of NCG interference in the steam cap and injection and natural recharge impacts on the field. These insights and the updated conceptual understanding of the Salak geothermal system coupled with reservoir simulation have provided a credible forecast of the Salak reservoir’s future performance for decision-makers to have the necessary confidence to fund the injection realignment project. Additionally, the refined conceptual model provides the reservoir management team with a means to plan and target development make-up wells and effectively focus future data gathering and reservoir monitoring activities.