Geochemical Changes in Response to Production and Reinjection for Palinpinon-I Geothermal Field, Negros Oriental, Philippines

Abstract

Chernical changes observed for producticn wells since the commissioning of the 112.5MWe Palinpinon-I Power station (May, 1983) have been attributed toreinjection fluid returns and in some cases, localised pressure drawdown. Although there is clear evidence for a mass front of reinjecticn fluid to the production sector, no thermal front has as yet been confirmed. A field manaqement strategy has developed in an attempt to minimise reinjection fluid returns. Chloride concentrations in separated water have been successfully used to trace. and quantify reinjection fluid returns on an individual production well and field basis. The magnitude of this and other sources of recharqe depend upon Power station load, productior. and reinjection well configurations and production well status or discharge history. Silica concentrations have remained controlled by quartz solubility despite large increases in reservoir chloride. Calcium and sulphate responses indicated dissolution of Ca-bearing minerals within the reinjection sectcr and re-deposj.tion of anhydrite as fluid migrated away from the reinjection sector.