The Natural State Model of the Reservoir of the Mindanao I Geothermal Field

Abstract

The Mindanao I Geothermal Field is a typical andesitic volcano-hosted hydrothermal system in high relief topography. The conceptual model of the field suggests that the upwelling fluids are beneath the Sandawa Collapse northwest of the Mt. Apo peak. A reservoir of two-phase fluids exists above -250 to 0 m RSL from where boiling is postulated to occur. The out flowing fluids move towards the northwest through the various structures in the Marbel Corridor. They are diverted to the north by the cold Matingao Block before being discharged to the surface through the chloride springs of Imba, Marbel and Sisiman.

A three-dimensional natural state model of the reservoir was developed using the MULKOM computer code. The stea4 state model was calibrated against the field data. The best fit natural state closely corresponds to the conceptual model of the field. The model suggests that the convective system of the reservoir has a natural recharge of 70 kg/s with an enthalpy of 1600 kJ/kg.