Geothermal System and Conceptual Model of Songa-Wayaua, North Maluku, Indonesia.pdf

Songa-Wayaua geothermal area is one of the most interesting geothermal areas located in the Bacan Island, province of North Maluku. Surface thermal features in the Songa-Wayaua area consist of hot springs, fumaroles, mud pools, hot grounds, and rock alterations by temperature 65-103.5°C. 3D-surveys have been conducted in 2006 to identify the geothermal system and prospect area of Songa-Wayaua. A 3D-inversion model from gravity data revealed a geothermal system concentrated under Songa graben structure, between Bukit Lansa dan Bukit Pele. The two bodies are the youngest volcanic rocks and estimated as the heat source of geothermal systems in this area.

Geological data of Songa-Wayaua indicate impermeable rocks that have properties with argilic clay mineral (argilic clay cap) on alteration zones near the hot springs. Altered rocks occur in the Quaternary volcanic lava units and Sibela metamorphic rocks. This alteration is also reflected in the zone of magnetic anomalies, which are characterized by zones of demagnetization around manifestation of Babale Lansa, Pelepele and Padopado. Low apparent resistivity (<15 ohm-m) also indicate the presence of a layer of rock alteration due to geothermal fluid interaction with the surrounding rock.

A reservoir is possibly formed in Cretaceous Metamorphic rocks, below the volcanic units, where the volcanic unit itself also has the possibility of becoming a shallow reservoir. The rock which has a density of 2.83 gr/cm3 is considered suitable to be a reservoir because it has undergone a process of deformation in the Miocene until the Pleistocene period that caused a pattern of intense fractures and permeability.