Modelling Application to Estimate the Thermal Output of Weh Island, Nangro Aceh Darussalam, Indonesia

Abstract

Weh Island is located in the westernmost part of Indonesia. It has a geothermal field in the south part and a high intensity of submarine volcanic activities in its middle coastal area due to the existence of the active Sumatran Fault and current volcanism, producing hydrothermal mineralisation in the fault zone. Submarine volcanic activities controlled by normal faults and a graben are observed in Sabang Bay, located near the centre of Weh Island. These submarine volcanic activities are indicated by the many appearances of submarine fumaroles (white smokers) in the seafloor vicinities of Serui and Pria Laot and other bodies of water in Weh Island. There are also surface thermal features that appear in the coastal area in the forms of hot springs, fumaroles, solfataras, hot ground, and hot mud pools. Furthermore, the geothermal system emerging at the south part of the island is also indicated by the appearance of surface manifestations like hot spring, fumaroles, and hot ground at Jaboi. This project develops a new reservoir model of Weh Island and an uncertainty quantification framework for estimating the total thermal output as a result of the island’s volcanic activities. The new model presented consists of the 3D geological model developed in Leapfrog Geothermal combined with the natural state reservoir model simulated using the new geothermal simulator Waiwera. The uncertainty quantification framework adjusts the model parameters affecting both geothermal and volcanic-hydrothermal upflows and constrains them using information regarding Weh Island’s submarine volcanic activities and the surface thermal manifestations. The air-water equation of state is used in the model to enable the model to include the vadose zone, thus a comprehensive representation of the system up to the surface can be made.