Numerical Modeling of the Songa-Wayaua Geothermal Reservoir Incorporating Seawater Intrusion Effects

Abstract

The Songa-Wayaua Geothermal Working Area (GWA), located in South Halmahera, North Maluku, is a high-enthalpy geothermal system with planned development for 2 × 5 MW power generation. Despite considerable progress in exploration and early-stage modeling, challenges remain in accurately simulating subsurface behavior near the coastline, particularly with regard to seawater intrusion and its impact on reservoir performance. This study presents the development of an updated numerical reservoir model using the Brynhild module within the Volsung geothermal simulation platform. By integrating geological, geophysical, and geochemical data, a refined 3D conceptual model was constructed in Leapfrog and subsequently imported into Brynhild. The model incorporates a multi-component equation of state (H₂O + CO₂ + NaCl) to capture the thermodynamic effects of saline intrusion. Boundary conditions and reservoir properties were carefully calibrated to replicate natural state conditions and surface manifestations. Simulation results successfully reproduce pre-exploitation temperature and pressure profiles and demonstrate the extent and direction of seawater intrusion. History matching mass flow and chloride concentrations further validates the model’s ability to represent dynamic reservoir behavior. This integrated modeling approach provides critical insights for sustainable geothermal development in coastal settings.