The Geochemical Response of the Tongonan Geotheral Reservoir (Philippines) After 18 Years of Production

Abstract

The present geochemical state of the Tongonan reservoir was evaluated to provide an updated h ydrogeochemical model of the field. Pressure drawdown plays a major role in the reservoir processes that are continuously observed. The brine recharge to the northwestern part of the field has decreased due to the decline of brine injection load. As a result, several production wells of the northern and central sectors, which have limited recharge from the deep hot source or from peripheral waters, are discharging almost pure dry steam. C02 concentrations of the production wells are among the highest in the whole field. To sustain the reservoir, separated brine from the South Sambaloran sector is being injected in the Tongonan-I sector to provide mass recharge to the dry wells. At present, only one production well has shown indications of brine returns. By the end of year 2002, about 270 kg/s of power plant condensate will be injected in the northernmost injection sink which is expected to provide mass recharge to the neighboring production wells. In the northeastern margin of the field, the recharge from meteoric waters has stabilized. The southeastern sector is receiving recharge from injected brine and acid-sulfate waters making it the only remaining water-dominated region of the field.