Geochemistry of the Palimpinon Geothermal Field, Southern Negros, Philippines

Abstract

Areal patterns of aquifer fluid chemistry at Palimpion are consistent with patterns of gas chemistry in indicating that the principal source of deep fluid feeding the production zones of existing wells lies to the south of the central part of the reservoir. Enthalpy chloride mixing relationships indicate a deep parent fluid at about 310°C with about 3,800 mg/1 C1. Boiling and mixing processes have produced variations of chloride within the reservoir from about 3,000 to 4,100 mg/1. Fluids at the western end of the reservoir appear to have evolved principally through mixing of the deep fluid with dilute recharge, whereas along the eastern fringe of the central area mixing has followed concentration by boiling. The least evolved fluids are tapped by wells which lie along a N-S trend which enters the central part of the reservoir from the south. This trend is fairly well defined by contours of the chemical geothermometers, Na/K, and C1. It may be related to structures along which the principal upwelling into the reservoir, and/or feeding from the south , is occurring.