Indonesia is a country blessed with huge high temperature geothermal resources. Many volcanic geothermal systems characterized by the occurrence of high temperature fumaroles, magmatic gases such as H2S and SO2 as well as solfataras on the summit of active volcanoes can be found in this country. Arjuno-Welirang is one of the volcanic geothermal systems found in Java island.
(a) Java island in Indonesian scale, showing Arjuno-Welirang is one of the volcanic geothermal systems found in Java island. (b) Faults may affect the geological structure development in Arjuno-Welirang area. (Source: Journal of Asian Earth Sciences, Resistivity characterization of the Arjuno-Welirang volcanic geothermal system (Indonesia) through 3-D Magnetotelluric inverse modeling, Yunus Daud et al, 2019)
The Arjuno-Welirang geothermal area is located in East Java, Indonesia. Mount Arjuno-Welirang lies about 50 kilometers south of Surabaya, and 20 kilometers north of Malang. Administratively, it is located in four regencies, namely Mojokerto, Pasuruan, Malang and Batu City. In 2014 by the Ministry of Energy and Mineral Resources (ESDM), officially it was known as WKP (Working Geothermal Area) Gunung Arjuno Welirang. To reach Arjuno Welirang, we can travel from Jakarta to Malang with a flight, then proceed by road via Jl. Junggo or Jl. Ir. Sukarno. In addition, we can take a flight from Jakarta to the city of Surabaya, then continue by road trip via Jl.Tol Surabaya-Gempol.
Mount Arjuno-Welirang (source: https://medium.com/)
In the Arjuno-Welirang geothermal area, the Arjuno, Welirang and Anjasmoro volcanic complex is dominated by quaternary volcanic rocks and a complex geological structure. Several impressive surface thermal manifestations are found in the area, including a high temperature solfataric-fumarole (about 137°C) on the top of Mt. Welirang and also bicarbonate hot springs with a temperature range of 39–55°C in the northern and western parts. The occurrence of the high temperature solfataric-fumarole with high magmatic gas contents indicates that the Arjuno-Welirang geothermal area can be classified as a volcanic geothermal system.
Exploration studies continue to be conducted at the Arjuno-Welirang complex. Geoscience surveys, such as geology, geochemistry and geophysics have produced some data to investigate the potential of geothermal energy in the area. The results of research carried out by PT NewQuest Geotechnology in collaboration with Universitas Indonesia and Center of Mineral, Coal and Geothermal Resource of Ministry of Energy and Mineral Resource (PSDMBP-ESDM) revealed that the main reservoir below Mt. Welirang is located at elevation of about 1000 m for the shallowest level, or 2000 m from the summit. Furthermore, the subsurface temperature at this depth estimated from the CO2-gas geothermometry is about 260°C. A conceptual model was built to visualize the geothermal system of the Arjuno-Welirang prospect area by integrating the geosciences data. The development plan of WKP Gunung Arjuno Welirang will be implemented in 2025 with an installed capacity of 110 MW.
Conceptual model of the Arjuno-Welirang geothermal prospect area (Source: Journal of Asian Earth Sciences, Resistivity characterization of the Arjuno-Welirang volcanic geothermal system (Indonesia) through 3-D Magnetotelluric inverse modeling, Yunus Daud et al, 2019)