Abstract

The Tiwi geothermal field began commercial electric power generation in 1979. From 1979 to 1982, six generating units with a total capacity of 330 megawatts were commissioned in the field. During this period of maximum mass withdrawal, major changes in the reservoir occurred. A liquid-dominated geothermal system, the Tiwi Field produces a mixture of steam and brine. As an effect of exploitation, two-phase zones have formed in some areas of the field; some wells now produce 100% steam. In other areas, wells have become uproductive because of the influx of cold ground water into the reservoir.

This paper describes the encroachment of the cold water into the reservoir and the operational adjustments that were made to minimize its impact. Geochemical sampling and analyses are used to periodically update the progress of the cold water. The source and movement of the cold water have also been defined with the help of tracer surveys. Field development strategies are now focused on areas that are least affected by the encroaching cold water.